[ Next: Getting Started with JGNAT | Previous: Top | Up: (dir) ]

# About This Guide

This guide describes the features and the use of JGNAT, the Ada 95 development environment for the Java platform. This guide also explains how to use the Java API from Ada and how to interface Ada and the Java programming language.

Please note that, unless you are using GLIDE (the GNAT IDE), all JGNAT tools are command-line tools. This means that they must be invoked from the shell (UNIX) or DOS window (Microsoft Windows).

Please consult file `jgnat-1.1p-README.txt` for JGNAT installation information. The section "Problem Reports" in that file explains how to report problems that you may find in JGNAT.

Before reading this manual you should be familiar with the GNAT User Guide as a thorough understanding of the concepts and notions explained there is needed to use JGNAT effectively.

- What This Guide Contains:

- What you should know before reading this guide:

- Related Information:

- Conventions:

[ Next: What you should know before reading this guide | Previous: About This Guide | Up: About This Guide ]

## What This Guide Contains

This guide contains the following chapters:

- [Getting Started with JGNAT], gives an overview of JGNAT and its tools and explains how to compile and run your first Ada program for the Java platform.
- [Ada & Java Interoperability] explains how the Java API and the services of any JVM class can be used from Ada. This section also explains how Ada services can be exported to Java programmers.
- [Viewing Class Files with jvmlist], describes `jvmlist`, a utility to disassemble a JVM `.class` file to view its contents: bytecode, contant pool (i.e. symbol table), debugging info, etc. This utility can also embed the original source code into the assembly listing.
- [Stripping Debug Info with jvmstrip], describes `jvmstrip` a utility that strips a `.class` file, removing all of its debugging info to reduce the file size.
- [Building Archives with jarmake], describes the `jarmake` tool to make a single `.jar` file for an application built with JGNAT. This is useful when you want to ship a self-contained application built with JGNAT to someone who does not have JGNAT installed. This tool is very useful useful when creating "gnapplets" (GNAT applets, see [Creating Gnapplets with JGNAT]).
- [Using the Java API with jvm2ada], describes the `jvm2ada` interfacing tool that takes any JVM `.class`, `.zip` or `.jar` files as input and generates Ada package specs as output. The resulting Ada specs can be used by Ada programs to interface to Java.
- [Java-Specific Pragmas] explains some special pragmas that have been introduced to support certain aspects of interfacing between Ada and Java.
- [Mapping Java into Ada] gives details on how the Java API and, in general, any Java class spec is mapped into an Ada package specification by the `jvm2ada` tool.
- [Creating Gnapplets with JGNAT], explains how you can create "gnapplets" (GNAT applets).
- [Debugging Ada Programs], describes how to run and debug Ada programs.

[ Next: Related Information | Previous: What This Guide Contains | Up: About This Guide ]

## What You Should Know Before Reading This Guide

Before reading this document readers should be familiar with the GNAT User Guide and have a conceptual understanding of the Java technology.

[ Next: Conventions | Previous: What you should know before reading this guide | Up: About This Guide ]

## Related Information

For further information about GNAT, Ada 95, and the Java technology, we recommend consulting the following documents:

- GNAT User Guide, contains introductory and reference material for the GNAT development environemnt.
- Ada 95 Language Reference Manual, contains all reference material for the Ada 95 programming language.
- The Java Tutorial: Object-Oriented Programming for the Internet, 2nd edition, by Mary Campione and Kathy Walrath, published by Addison Wesley.
- The Java Virtual Machine Specification, by Tim Lindholm and Frank Yellin, published by Addison Wesley.

[ Previous: Related Information | Up: About This Guide ]

## Conventions

Following are examples of the typographical and graphic conventions used in this guide:

- `source code`, and `utility program names`.
- `Option flags`.
- `File Names`.
- Variables.
- Emphasis.
- [optional information or parameters]
- Examples are described by text

      and then shown this way.

Commands that are entered by the user are preceded in this manual by the "`$` " characters (dollar sign followed by space). If your system uses this sequence as a prompt, then the commands will appear exactly as you see them in the manual. If your system uses some other prompt, then the command will appear with the `$` replaced by whatever prompt character you are using.

[ Next: Ada & Java Interoperability | Previous: About This Guide | Up: (dir) ]

# Getting Started with JGNAT

- Overview:

- JGNAT Tools:

- Java Development Kits that you can use with JGNAT:

- Compiling Your First Application with JGNAT:

[ Next: JGNAT Tools | Previous: Getting Started with JGNAT | Up: Getting Started with JGNAT ]

## Overview

The Java(TM) technology, introduced by Sun Microsystems, is a paradigm whose goal is to add platform-independent programming flexibility to Internet, Intranet and Extranet applications, embedded devices such as Internet appliances, consumer electronics, smart cards, etc.

The Java technology comprises, a simple object-oriented programming language (Java), a comprehensive set of libraries (Java API), and a virtual machine (JVM) offering the same object code interface on all platforms (bytecode).

Although the Java environment comes with a default programming language, this language is not a fundamental component of the technology. Any programming language that can be mapped onto the JVM can be used to develop Java applications.

The JGNAT system offers a complete Ada 95 programming environment for the Java platform. In addition to a bytecode compiler, binder and linker, JGNAT comprises a Java-to-Ada 95 binding generator which produces the Ada 95 specs of the services contained in any Java `.class` file or API. In addition to all of the conventional GNAT tools, a bytecode disassembler and a `.class` file stripper are also provided with JGNAT.

Furthermore, because the `.class` files generated by the JGNAT compiler are fully compliant with Sun's standard, the user can employ any JVM to run Ada applications, any JVM debugger to debug Ada code, and can use any of the Java tools that operate on `.class` files (e.g. `jar`, `javap`, etc.).

As a side note, the JGNAT system is implemented in Ada 95 and its sources are available under the GPL.

[ Next: Java Development Kits that you can use with JGNAT | Previous: Overview | Up: Getting Started with JGNAT ]

## JGNAT Tools

Most JGNAT tools are regular GNAT tools that have been slightly adapted for use with JGNAT. They are used in the same fashion as their corresponding GNAT equivalent. These tools are:

- `jgnat`: the JGNAT compiler, compiles an Ada unit into one or more JVM `.class` files.
- `jgnatbind`: the JGNAT binder, generates an Ada source file containing the elaboration code for the Ada application to run.
- `jgnatlink`: the JGNAT linker, compiles the source file generated by `jgnatbind`. `jgnatlink` provides no linking capabilities since the linker is directly embedded into the JVM. To gather the `.class` files of an application into a single file, one can use the `zip` or `jar` commands provided with your Java Development Kit.
- `jgnatmake`: the JGNAT automatic make program, automatically determines the set of sources needed by an Ada compilation unit, and executes the necessary compilations, binding, and link.
- `jgnatls`: the JGNAT library browser, displays information about compiled units, including dependences on the corresponding sources files, and consistency of compilations.
- `jgnatfind`: the JGNAT find utility, provides an easy way to locate the declaration and references for an Ada entity.
- `jgnatxref`: the JGNAT cross-referencer, allows you to generate a full report of all cross-references in a given set of Ada units.
- `jgnatpsta`: the JGNAT utility to print the JGNAT version of package Standard.

The GNAT tools that are completely target independent (such as `gnatchop`, `gnatprep`, `gnatelim`, etc.) have not been provided with JGNAT since they are available in the regular GNAT installation and you can use them directly.

Please note that, unless you are using GLIDE (the GNAT IDE), all JGNAT tools are command-line tools. This means that they must be invoked from the shell (UNIX) or DOS window (Microsoft Windows).

The JGNAT tools which have been specifically developed for JGNAT are:

- `jvmlist`: The JGNAT disassembler, (see [Viewing Class Files with jvmlist]) disassembles a JVM `.class` file to view its contents: bytecode, constant pool (i.e., symbol table), debugging info, etc. This utility will also embed the original source code into the assembly listing. This utility is independent of the original programming language and works equally well on programs containing a mixture of Ada and Java code.
- `jvmstrip`: The JGNAT strip utility, (see [Stripping Debug Info with jvmstrip]) is a utility that strips a `.class` file, removing all of its debugging info to reduce file size. This tool is also programming-language independent.
- `jarmake`: The JGNAT archiver tool, (see [Building Archives with jarmake]) takes `.class` files as input and recursively collects into an uncompressed zip archive all the `.class` files needed by the `.class` files specified on the command line. This tool can be used to prepare self-standing applications or gnapplets that you can ship. This tool is programming-language independent.
- `jvm2ada`: The JGNAT interfacing tool, (see [Using the Java API with jvm2ada]) takes `.class` files, or zip archives as input and generates Ada package specifications as output. The resulting Ada package specs can be `with`-ed by Ada programs to interface to Java services.

[ Next: Compiling Your First Application with JGNAT | Previous: JGNAT Tools | Up: Getting Started with JGNAT ]

## Java Development Kits that you can use with JGNAT

Because JGNAT generates class files that are fully compliant with Sun's JVM standard, you can use any Java Virtual Machine and bytecode tools that meet the Sun Java platform standard.

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## Compiling Your First Application with JGNAT

Before trying out JGNAT, make sure you first read the section on installing JGNAT in the file `jgnat-1.1p-README.txt`, which explains about setting the variables PATH and CLASSPATH on your system.

To compile the following "`Hello JGNAT`" program put the following in file `hello.adb`:

    with Ada.Text_IO; use Ada.Text_IO;
    procedure Hello is
    begin
       Put_Line ("Hello JGNAT.");
    end Hello;

then type:

    $ jgnatmake hello

This command will generate file `hello.class`. To run it, assuming you are using Sun's JDK (Java Development Kit), you can just type

    $ java hello

It's as simple as that. To compile more complex Ada applications use `jgnatmake` as usual. If you want to use the JGNAT compiler, binder, and linker separately, you will need to individually invoke the appropriate `jgnat`, `jgnatbind` and `jgnatlink` commands.

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# Ada & Java Interoperability

One aspect of Java that makes it an interesting platform is its growing set of API classes. It is therefore fundamental that the API be made available to the Ada programmer transparently. It is also important that the Ada programmer be able to write libraries or APIs for the Java platform in Ada, and that these libraries be easily usable in any Java application. JGNAT guarantees full interoperability between Ada and Java.

To achieve this goal, constructs that can appear in a Java class at the specification level are mapped to Ada either by means of a corresponding Ada feature or by using an implementation-defined Ada pragma.

In addition we have taken great care that the mapping from Java to Ada is completely automatic. This means that JGNAT comes with no Ada bindings for the Java API, but instead provides a tool (see [Using the Java API with jvm2ada]) which is able to produce Ada specifications from any set of JVM `.class` files.

- Importing Java Services to Ada:

- Exporting Ada Services to Java:

[ Next: Exporting Ada Services to Java | Previous: Ada & Java Interoperability | Up: Ada & Java Interoperability ]

## Importing Java Services to Ada

To access the services provided by the Java API or by any set of JVM `.class` files, you should proceed as follows:

1. If your Java code is in source form, compile it using any Java compiler.
2. If you just want to import a variable or a subprogram from a Java class use `pragma Import` (see [Pragma Import Java]) in the Ada code where you want to import the Java service.
3. More generally, you can use the `jvm2ada` utility to produce the Ada specs (containing the appropriate Java-specific pragmas) for the `.class`, `.zip`, or `.jar` files containing the Java services you would like to use from Ada (see [Using the Java API with jvm2ada]). Note that `jvm2ada` preserves, in the generated Ada specs, the names of the original Java services (for a detailed explanation of the Java to Ada mapping see [Mapping Java into Ada]).
4. `with` the needed Ada specs and use their services as usual.

It's as simple as that.

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## Exporting Ada Services to Java

To export a set of Ada services to Java you should:

1. Use `pragma Export` and other Java interfacing pragmas inside the Ada code (see [Java-Specific Pragmas]). This gives you complete control of what is being generated and allows you to decide very precisely what the exported services look like on the Java side.
2. Compile your Ada code with the JGNAT compiler.
3. Use `javap` to display the spec of the `.class` files generated by JGNAT whose services you would like to use in your Java code.

[ Next: Stripping Debug Info with jvmstrip | Previous: Ada & Java Interoperability | Up: (dir) ]

# Viewing Class Files with `jvmlist`

The `jvmlist` tool takes JVM `.class` files as input (directly or regrouped in an uncompressed `.zip` or `.jar` file) and disassembles it to view its contents: bytecode, constant pool (i.e., symbol table), debugging info, etc. This utility can also embed the original source code in the assembly listing. `jvmlist` is independent of the original programming language and works equally well on programs containing a mixture of Ada and Java code.

- Running jvmlist:

- Switches for jvmlist:

[ Next: Switches for jvmlist | Previous: Viewing Class Files with jvmlist | Up: Viewing Class Files with jvmlist ]

## Running jvmlist

The form of the `jvmlist` command is

    jvmlist [switches] file [file ... file]

where file can be one of the following:

- the name of a `.class` file (possibly without the `.class` suffix);
- the name of an uncompressed zip archive (in this case the `jvmlist` command applies to all `.class` files within the archive);
- the name of a `.class` file within an uncompressed zip archive
  (e.g. `rt.jar/java/lang/Object.class`).

File names can be prefixed with directory information.

The output of `jvmlist` contains a listing of all the fields and methods declared inside the `.class` file, in addition to various other class information such as the class it extends, the interfaces it implements, etc.

If you select switch `-c`, then `jvmlist` will also print the bytecode for each method. The bytecode mnemonics used by `jvmlist` are the same as those documented in Sun's JVM book The Java Virtual Machine Specification by Lindholm and Yellin. If you select switch `-c`, `jvmlist` will also embed the original source code in the bytecode. For now, `jvmlist` only looks for source files in the current directory.

[ Previous: Running jvmlist | Up: Viewing Class Files with jvmlist ]

## Switches for jvmlist

The following switches are available with the `jvmlist` utility:

`-c`
  Display bytecode. By default `jvmlist` does not display the bytecode of each method. This switch specifies that bytecode should be displayed.
`-g`
  Embed source code. This switch implies `-c` and embeds the original source code within the disassembled bytecode. If the input `.class` file does not contain source file information, or if the source file cannot be located in the current directory (the one where `jvmlist` was invoked), then this switch is equivalent to `-c`.
`-l`
  Display line number tables.
`-p`
  Display the constant pool.
`-t`
  Display local variable tables.
`-v`
  Verbose. Outputs the name of each class file for which an Ada spec is generated.
`-V`
  Very verbose. Implies -v. Each item that is encountered in a zip or jar file is listed on the screen. Class files are preceded with a `->`, other items are listed with a message saying that the item is skipped. Only class files whose name is listed twice (one preceded with a `->` and the following one without the `->`) have a corresponding Ada spec generated for them, other class files are ignored (because for instance they are not public classes).

[ Next: Building Archives with jarmake | Previous: Viewing Class Files with jvmlist | Up: (dir) ]

# Stripping Debug Info with `jvmstrip`

The `jvmstrip` tool takes a `.class` files as input (directly or packaged in an uncompressed `.zip` or `.jar` file) and strips off all of its debugging info to reduce its size. This utility is independent of the original programming language and works equally well on programs containing a mixture of Ada and Java code.

- Running jvmstrip:

- Switches for jvmstrip:

[ Next: Switches for jvmstrip | Previous: Stripping Debug Info with jvmstrip | Up: Stripping Debug Info with jvmstrip ]

## Running jvmstrip

The form of the `jvmstrip` command is

    jvmstrip [switches] file [file ... file]

where file can be one of the following:

- the name of a `.class` file
- the name of an uncompressed zip archive (in this case the `jvmstrip` command applies to all `.class` files within the archive);

File names can be prefixed with directory information.

The output of `jvmstrip` is a stripped `.class` file which replaces the original input file. If the input is an archive, then all of the `.class` files within the archive are stripped and the updated archive replaces the input file.

[ Previous: Running jvmstrip | Up: Stripping Debug Info with jvmstrip ]

## Switches for jvmstrip

The following switches are available with the `jvmstrip` utility:

`-v`
  Verbose.

[ Next: Using the Java API with jvm2ada | Previous: Stripping Debug Info with jvmstrip | Up: (dir) ]

# Building Archives with `jarmake`

When building an Ada application with JGNAT, a number of JVM `.class` files are generated. In addition to potentially being numerous, the generated classes depend on the JGNAT library `jgnat.jar` which is installed with JGNAT.

If you need to ship your Ada application or gnapplet to people who do not have JGNAT installed this can be cumbersome as you would need to ship the `.class` files of your application along with `jgnat.jar`.

To automate such process we have provided `jarmake`, the JGNAT archiver tool. `jarmake` takes `.class` files as input and recursively collects into an uncompressed zip archive all the `.class` files needed by the `.class` files specified on the command line. This tool can be used to prepare self-standing applications or gnapplets.

This utility is independent of the original programming language and works equally well on programs containing a mixture of Ada and Java code.

- Running jarmake:

- Switches for jarmake:

[ Next: Switches for jarmake | Previous: Building Archives with jarmake | Up: Building Archives with jarmake ]

## Running jarmake

The form of the `jarmake` command is

    jarmake [switches] file [file ... file]

where file can be one of the following:

- the name of a `.class` file
- the name of an image, sound or any other file that you want to bundle with your application.

File names can be prefixed with directory information.

The output of `jarmake` is an uncompressed zip archive containing the files specified on the command line along with the `.class` files they recursively reference.

[ Previous: Running jarmake | Up: Building Archives with jarmake ]

## Switches for `jarmake`

The following switches are available with the `jarmake` utility:

`-Lzip-archive`
  When searching for `.class` files, look in the uncompressed zip archive zip-archive.
`-j`
  Do not skip `.class` files in the Java API. By default `jarmake` skips all the `.class` files in the Java API. By using this switch you are asking `jarmake` to include Java API classes in the output zip archive. If you set this flag you should also provide a `-L` flag giving the location of the Java API zip archive.
`-k`
  Keep going even if not all of the `.class` files are found. By default, `jarmake` will stop if it cannot find all the needed `.class` files. By setting this switch `jarmake` will emit a warning message when it cannot find a `.class` file it is looking for and will continue.
`-n`
  Do not include the `.class` files of the JGNAT library `jgnat.jar` in the output archive. By default these files are included in the output archive so that the the archive is autonomous.
`-o zip-archive`
  Name of the output uncompressed zip archive. If this switch is not specified, then the default name is `gnapplet.jar`.
`-q`
  Quiet.
`-v`
  Verbose.

[ Next: Java-Specific Pragmas | Previous: Building Archives with jarmake | Up: (dir) ]

# Using the Java API with `jvm2ada`

The `jvm2ada` tool takes JVM `.class` files as input (directly or regrouped in an uncompressed `.zip` or `.jar` file) and generates Ada specs as output.

- Running jvm2ada:

- Switches for jvm2ada:

- Running jvm2ada on the Java API:

- Parameter Names and Source Search Paths:

- Class File Search Paths:

- Identifier Mangling:

[ Next: Switches for jvm2ada | Previous: Using the Java API with jvm2ada | Up: Using the Java API with jvm2ada ]

## Running `jvm2ada`

The form of the `jvm2ada` command is

    jvm2ada [switches] file [file ... file]

where file can be any of the following:

- the name of a `.class` file (possibly without the `.class` suffix);
- the name of an uncompressed zip archive (in this case the `jvm2ada` command applies to all `.class` files within the archive);
- the name of a `.class` file within an uncompressed zip or jar archive
  (e.g. `rt.jar/java/lang/Object.class`).

File names can be prefixed with directory information.

The output of `jvm2ada` is an Ada source file for each `.class` file processed. The Ada source file contains a package spec giving the Ada declaration for the services exported by the corresponding `.class` file. The name of the Ada package is obtained by concatenating the name of the Java class to the name of the Java package containing the class. As an example, a Java class `someName` occurring within Java package `some.pack` yields the Ada package `some.pack.someName` and is in a file named `some-pack-somename.ads`.

Unless switch `-o` is used (see [Switches for jvm2ada]), the Ada files generated are placed in the directory where the `jvm2ada` command is invoked.

[ Next: Running jvm2ada on the Java API | Previous: Running jvm2ada | Up: Using the Java API with jvm2ada ]

## Switches for `jvm2ada`

The following switches are available with the `jvm2ada` utility:

`-Izip-archive`
  When looking for a source file (to find the parameter names of a Java method), search the uncompressed zip archive zip-archive. See [Parameter Names and Source Search Paths], for details. (This switch is not yet supported.)
`-Lzip-archive`
  When searching for `.class` files, look in the uncompressed zip archive zip-archive. See [Class File Search Paths], for details.
`-k`
  Keep original JVM identifiers. By default, identifiers encountered in a JVM .class file are mangled whenever needed to turn them into proper Ada identifiers. When this switch is set, identifiers are left as is in the generated Ada package spec. See [Identifier Mangling], for details.
`-o dir`
  Output to dir. Put all generated Ada source files into directory dir rather than the current directory.
`-q`
  Quiet.
`-s`
  Map Sun-specific classes into Ada specs. By default, Sun's classes are not mapped into Ada even if they are public, because they are typically not part of the API at hand (certainly they are not part of the Java API, even though the corresponding jar file contains them). Sun's classes are the classes in packages `sun`, `sunw`, and `com.sun`.
`-v`
  Verbose.
`-w`
  Overwrite existing file names. Normally `jvm2ada` regards it as a fatal error if there is already a file with the same name as a file it would otherwise output. This switch bypasses this check, and any such existing files will be silently overwritten.

[ Next: Parameter Names and Source Search Paths | Previous: Switches for jvm2ada | Up: Using the Java API with jvm2ada ]

## Running jvm2ada on the Java API

To be able to access the Java API you need to process it to generate an Ada package spec for each public class in the API. To do this you need to locate the zip or jar archive containing all class files of the Java API (for instance in Sun's Windows JDK 1.2.2 this archive is located in java-dir`\jdk1.2.2\jre\lib\rt.jar`, where java-dir is the JDK 1.2.2 installation directory) and simply type:

    $ cd your-favorite-dir
    $ jvm2ada java-dir\jdk1.2.2\jre\lib\rt.jar

This will create, in directory your-favorite-dir, an Ada package spec for each public Java class. If you would like to output the Ada specs in some other directory use `jvm2ada` switch `-o`.

Please note that because of a limitation of `jvm2ada` (see [Identifier Mangling]), the following Ada specs have ben edited so that they can compile:

- `java-awt-image-componentsamplemodel.ads`: field `numBands` was renamed into `numBands_C` because the parent type of `ComponentSampleModel` has also a field named `numBands`.
- `javax-swing-jcolorchooser.ads`: field `accessibleContext` was renamed into
  `accessibleContext_C` because the parent type of `JColorChooser` has also a fieldnamed `accessibleContext`.
- `javax-swing-jfilechooser.ads`: field `accessibleContext` was renamed into
  `accessibleContext_C` because the parent type of `JFileChooser` has also a fieldnamed `accessibleContext`.

[ Next: Class File Search Paths | Previous: Running jvm2ada on the Java API | Up: Using the Java API with jvm2ada ]

## Parameter Names and Source Search Paths

Note: Only point 2. below is implemented.

When generating the Ada spec for a `.class` file, `jvm2ada` tries to preserve the original names of method parameters. If the `.class` file was compiled enabling the generation of debugging tables (switch `-g` in Sun's JDK `javac` compiler), parameter names are stored in the `.class` file. If not `jvm2ada` proceeds as follows:

1. If the name of the original source file is present in the `.class` file, `jvm2ada` tries to locate this source by looking at the uncompressed zip archives specified by the `-Izip-archive` switches, in the order in which these switches occur. Once found, `jvm2ada` uses the source file to locate parameter names. If the original source is not around you can always communicate parameter names by creating a Java source file containing the appropriate method specs. For instance to give the names of the parameters of method `someMethod` in class `someClass` in package `some_package` you could create the following source file:

       package some_package;
       //  You must provide the appropriate Java package for someClass

       public class someClass {
          public int someMethod (int someName, float anotherName) {}
          //  The methods for which you want to name the parameters must have the
          //  same signature as the methods found in the .class file. The body
          //  can be empty.
       }

2. If the appropriate source file cannot be located `jvm2ada` assigns arbitrary parameter names of the form `P1_`type, `P2_`type, etc. where type denotes the flattened type name for the corresponding parameter. The reason for appending type to the parameter name is to allow the Ada programmer to resolve possible overloading resolution conflicts of the following kind

       public class Base { }
       public class Deriv extends Base {
          public static void p (Base  obj) { ... }
          public static void p (Deriv obj) { ... }
       }

   The overloaded procedure `p` above are translated by `jvm2ada` to the following Ada specs:

       procedure p (P1_Base  : access Base.Typ'Class);
       procedure p (P1_Deriv : access Deriv.Typ'Class);

   The problem that arises is shown by the following example:

       type Deriv_Ref is access all Deriv.Typ'Class;
       Obj : Deriv_Ref := ...;
       procedure p (Obj);              --  Ambiguos call
       procedure p (P1_Base  => Obj);  --  OK
       procedure p (P1_Deriv => Obj);  --  OK

[ Next: Identifier Mangling | Previous: Parameter Names and Source Search Paths | Up: Using the Java API with jvm2ada ]

## Class File Search Paths

When processing a `.class` file, `jvm2ada` may need to locate other `.class` files. For instance, to know whether the JVM class being processed is a Java exception, `jvm2ada` must traverse the inheritance tree and must therefore locate the `.class` files of the ancestor classes.

If `jvm2ada` does not find the `.class` file it is looking for, then a warning message is emitted. The order in which `jvm2ada` searches `.class` files is given below.

1. If the `.class` file being processed belongs to an uncompressed zip archive, `jvm2ada` will look there first.
2. The uncompressed zip archives specified by a `-Lzip-archive` switch are searched next, in the order in which the `-L` switches occur.

[ Previous: Class File Search Paths | Up: Using the Java API with jvm2ada ]

## Identifier Mangling

`jvm2ada` retains, whenever possible, the identifiers it finds in the `.class` files it processes. This is not always possible, however, because Java's set of legal identifiers is bigger than Ada's. To address these issues `jvm2ada` proceeds as follows: If switch `-k` is set, the original identifiers found in the JVM .class are left unchanged. You will have to change these yourself in the generated packages if these are illegal Ada identifiers. If switch `-k` is not set then:

- Every identifier which is an Ada reserved word or any of the words "`Standard`", "`Ref`", "`Typ`", "`Arr`", "`Arr_2`", "`Arr_3`", is suffixed with `_K`. For instance, `Abort` is mapped to `Abort_K`.
- A single underscore is replaced by "`U`".
- A leading underscore is replaced by "`U_`".
- A trailing underscore is replaced by "`_U`".
- A letter "`U`" is placed between every two consecutive underscores.
- If two or more identifiers generated in an Ada spec lead to an Ada name conflict, then `jvm2ada` will add a trailing `_K` at the end of the second occurrence, a trailing `_K2` at the end of the third occurrence, a trailing `_K3` at the end of the fourth occurrence, etc. The cases currently caught are: identical variable names, identical variable and subprogram names, identical variable and child package name. More complex cases are not yet handled. In particular, we do not yet detect the case where we have two identical field names in a record `B` and a record `D` derived from `B`. In these cases you will have to revise the generated Ada spec to allow it to compile.

[ Next: Mapping Java into Ada | Previous: Using the Java API with jvm2ada | Up: (dir) ]

# Java-Specific Pragmas

The typical way to import services from Java classes is to use the `jvm2ada` tool to automatically generate the specification of the corresponding `.class` file. This specification contains the appropriate Java-specific pragmas.

In some cases you may wish to import just one routine to your Ada code or you may prefer to group certain services from multiple `.class` files into a single Ada spec (for instance if you are trying to provide a simplified view of the Java API).

In such cases it is useful to understand how the various Java-specific pragmas work. Another situation where you may have to use these pragmas explicitly is when exporting Ada services to Java.

This chapter introduces the features and pragmas that are needed for full support of interfacing between Java and Ada.

- Handling Circularities using With-Type Clauses:

- Creating Java Interfaces with Pragma Java_Interface:

- Using Java Interfaces:

- The Java_Constructor Pragma:

- Pragma Import Java:

- Pragma Export Java:

[ Next: Creating Java Interfaces with Pragma Java_Interface | Previous: Java-Specific Pragmas | Up: Java-Specific Pragmas ]

## Handling Circularities using With-Type Clauses

- Introduction:

- The With-Type Clause:

- Semantics of the With-Type Clause:

- With-Type and the -gnatX Compiler Switch:

- With-Type Example:

- A Word of Caution:

[ Next: The With-Type Clause | Previous: Handling Circularities using With-Type Clauses | Up: Handling Circularities using With-Type Clauses ]

### Introduction

A long-standing programming problem that is difficult to solve in Ada is that of creating mutually dependent package specifications. The problem is that Ada package specifications aren't allowed to depend on each other. There are various possibilities for working around this restriction in specific cases, generally involving levels of indirection and syntactically heavy programming idioms. However, these workarounds are too cumbersome for practical use, and certainly not appropriate in the context of interfacing to the Java API (which allows circular class definitions). A simple example of this occurs between the classes `java.lang.Object` and `java.lang.String`:

    public class Object {
       ...
       public String toString ();
    }

    public final class String {
       ...
       public static String valueOf (Object obj);
    }

Each class declares operations using a type declared in the other class. Clearly this can't be mapped directly into two independent Ada package specifications.

[ Next: Semantics of the With-Type Clause | Previous: Introduction | Up: Handling Circularities using With-Type Clauses ]

### The With-Type Clause

To support such mutual dependencies we have implemented a general-purpose feature called the with-type clause. The purpose of the with-type clause is to import the name of an access or tagged type defined in a separate package, while not requiring the package with the clause to depend (in the Ada semantic sense) on the other package.

The form of the with-type clause for access types is:

    with type package-name.access-type is access;

where package-name must denote an existing package containing an access type whose name is access-type. The access-type can be any access type declared inside the visible part of package-name's spec. It is a compile-time error if package-name's spec is not available or does not contain the access type access-type. A with-type clause is only allowed in the context clause of a package spec, that is, in the same location where `with` clauses can appear. If an explicit `with` clause for package-name appears in the same context clause as a with-type clause for package-name.access-type, then the with-type clause is superfluous and is ignored. Note that package-name must be a fully qualified name in the case of child packages.

The with-type clause can also be used for tagged types, and the syntax is:

    with type package-name.tagged-type is tagged;

In the tagged form of the with-type clause, the package-name must denote a package whose visible part contains a tagged type named tagged-type.

[ Next: With-Type and the -gnatX Compiler Switch | Previous: The With-Type Clause | Up: Handling Circularities using With-Type Clauses ]

### Semantics of the With-Type Clause

The semantic effect of giving the with-type clause is to make the specified type name available for use within the containing package, though the uses of such a type name are restricted.

In the access type case, the type name can only be used to declare formal parameter types and component types. However, since nothing is known about the designated type within the package specifying the with-type clause, no operations involving dereferencing pointers of the access type are permitted within the specification.

For the tagged type form of the clause, the type name can only be used in formal parameter declarations, for declaring access types, and as the prefix of the `Class` attribute (and the same restrictions apply to the name of the class-wide type).

In terms of elaboration dependencies, no dependency is introduced by the with-type clause. On the other hand, if a package spec `P` contains a with-type clause that names an access type in a package spec `Q`, then `P` depends on `Q`'s spec at the source file level. This means that if `Q`'s spec is updated then `P` needs to be recompiled.

[ Next: With-Type Example | Previous: Semantics of the With-Type Clause | Up: Handling Circularities using With-Type Clauses ]

### With-Type and the `-gnatX` Compiler Switch

Because the with-type clause is an extension to the Ada language, it is necessary to use the GNAT compile-time option `-gnatX` (or the `Extensions_Allowed` pragma) when compiling any unit that either uses this feature or depends on a unit that uses it.

For convenience, when using an Ada spec generated by `jvm2ada`, the use of option `-gnatX` is not necessary because `jvm2ada` inserts the appropriate `Extensions_Allowed` pragmas around the generated Ada sources.

[ Next: A Word of Caution | Previous: With-Type and the -gnatX Compiler Switch | Up: Handling Circularities using With-Type Clauses ]

### With-Type Example

Let's look at an example. Here are portions of the packages `java.lang.Object` and `java.lang.String` that uses this pragma:

    with type java.lang.String.Ref is access;
    package java.lang.Object is
       type Typ is tagged limited private;
       type Ref is access all Typ'Class;
       ...
       function toString (This : access Typ) return java.lang.String.Ref;
    end java.lang.Object;

    with java.lang.Object;
    package java.lang.String is
       type Typ is ...;
       type Ref is access all Typ'Class;
       ...
       function valueOf (Obj : access java.lang.Object.Typ'Class)
                        return java.lang.String.Ref;
    end java.lang.String;

A client of package `Object` wanting to use `toString` would have to write:

    with Java.Lang.Object;
    with Java.Lang.String; use Java.Lang;
    procedure Client is
       Obj : Object.Ref := ...;
       Str : String.Ref := toString (Obj);
       ...

Here is another example, where `with type` is used for access to array types.

    with type Class_B.Ptr is access;
    with type Class_B.Arr_Ptr is access;
    package Class_A is
       type Typ is record
          Val      : Integer;
          Link     : Class_B.Ptr;
          Arr_Link : Class_B.Arr_Ptr;
       end record;

       type Ptr is access Typ;
       type Arr is array (Natural range <>) of Ptr;
       type Arr_Ptr is access Arr;

       procedure Proc_A (P1 : Class_A.Ptr; P2 : Class_B.Ptr);
    end Class_A;

    with type Class_A.Ptr is access;
    with type Class_A.Arr_Ptr is access;
    package Class_B is
       type Typ is record
          Val      : Float;
          Link     : Class_A.Ptr;
          Arr_Link : Class_A.Arr_Ptr;
       end record;

       type Ptr is access Typ;
       type Arr is array (Natural range <>) of Ptr;
       type Arr_Ptr is access Arr;

       procedure Proc_B (P1 : Class_A.Ptr; P2 : Class_B.Ptr);
    end Class_A;

    with Class_A;
    with Class_B;
    procedure Client is
       P_A : Class_A.Ptr := new Class_A.Typ;
       P_B : Class_B.Ptr := new Class_B.Typ;
    begin
      Class_A.Proc_A (P_A, P_B);
      Class_B.Proc_B (P_A, P_B);
    end Client;

One important thing to note is that eventually there need to be normal with clauses for the units containing any types that are referenced via with-type clauses.

This should be checked by the compiler, but there are currently cases where this is not enforced and it is possible to dereference an access value even though the unit was only imported via a with-type clause. For now users must be aware of this and ensure that all units that use access values originating from such types make a real dependence on the package defining the type.

[ Previous: With-Type Example | Up: Handling Circularities using With-Type Clauses ]

### A Word of Caution

The specifics of the with-type feature may change in the future. The important capability of supporting mutually dependent packages via a feature like the with-type clause is currently being discussed by the ISO WG9-sponsored Ada Rapporteur Group. However, the current GNAT implementation may differ from the final, WG9-approved version, though it is similar in syntax and semantics to what is currently being proposed. Users are cautioned that this is not yet an approved extension to the Ada language and should be used judiciously.

[ Next: Using Java Interfaces | Previous: Handling Circularities using With-Type Clauses | Up: Java-Specific Pragmas ]

## Creating Java Interfaces: Pragma `Java_Interface`

Java offers a special kind of class called an interface. Interfaces provide a limited but useful form of multiple inheritance. A Java interface is basically an abstract class with no fields and whose methods are all abstract. Instead of inheriting from an interface, a Java class `C` is said to implement the interface, which means that `C` must provide an implementation for all of the abstract methods declared in the interface.

The key point to note about interfaces is that a class `C` can implement several interfaces at the same time, and this mechanism is orthogonal to the fact that `C` may be extending some other class.

To make a Java interface available to an Ada program we have provided the pragma `Java_Interface`. Its syntax is:

    pragma Java_Interface (type-name);

where type-name is the name of a type T declared earlier, immediately within the same declarative part where the pragma occurs, and where the type has the following characteristics that reflect the restrictions on Java interfaces:

1. T must be an abstract tagged type with a null record extension.
2. T must be derived from `java.lang.Object.Typ` (see [Java References and java.lang.Object]).
3. T must have an access discriminant named `Self` with `java.lang.Object.Typ'Class` as its designated type.
4. All of T's primitive operations must be abstract.
5. T must have Java `Convention`.

Here is an example of using pragma `Java_Interface`:

    with java.lang.Object;
    package Foo is
       type Typ (Self : access java.lang.Object.Typ'Class)
         is abstract new java.lang.Object.Typ with null record;
       pragma Java_Interface (Typ);

       type Ref is access all Typ'Class;

       procedure Proc (This : access Typ; Val : Integer) is abstract;
       function  Func (This : access Typ) return Integer is abstract;

    private
       pragma Convention (Java, Typ);
    end Foo;

[ Next: The Java_Constructor Pragma | Previous: Creating Java Interfaces with Pragma Java_Interface | Up: Java-Specific Pragmas ]

## Using Java Interfaces

In order to declare an Ada type that implements one or more Java interfaces it is necessary to use a simple programming idiom that is specially recognized by the compiler. This mechanism is not restricted for use only with types imported from Java, but can be applied to any Ada tagged type T.

The idiom consists in specifying a discriminant D for each Java interface Interf that type T implements. The type of D must be some access type whose designated type is Interf. Discriminants such as D are not represented by an actual field in the object, but rather serve as a symbolic shorthand to indicate the special characteristics of type T to the compiler.

As an example, the following package spec declares a type `Bar.Typ` which implements interface `Foo.Typ`:

    with Foo;
    package Bar is
       type Typ (Foo_I : Foo.Ref) is tagged record
          Field : Integer;
       end record;
       --  Discriminant Foo_I above signals that Bar.Typ implements the
       --  Foo.Typ interface (Foo_I stands for Foo Interface). The
       --  compiler does not create a field for Foo_I but marks the
       --  generated .class file as implementing interface Foo.Typ.

       procedure Proc (This : access Typ; Val : Integer);
       function  Func (This : access Typ) return Integer;
       --  Unless Bar.Typ is itself marked abstract, Bar.Typ must
       --  provide an implementation for subprograms Proc and Func.
       --  Right now if you omit these subprograms the JGNAT compiler will not
       --  complain, but when loading the .class file corresponding to Bar.Typ
       --  the JVM will halt execution with a verifier error.
    end Bar;

As mentioned in the example, unless T is abstract, T must provide an implementation for each of the abstract operations of the Interf interface (currently this check is not done by the JGNAT compiler but is caght later on by the JVM).

A second use of these special interface discriminants is to enable conversions between pointers to type T and pointers of its implemented interface types as the example below demostrates.

    with Foo;
    with Bar;
    package Client is
       X : Bar.Ref := new Bar.Typ (null);
       --  Create an object of type Bar.Typ. To satisfy Ada's semantic rules
       --  we must provide a value for Foo_I, but this value is ignored.

       Y : Foo.Ref := X.Foo_I;
       --  OK, upward conversion allowed, no checks.
       --  Referencing discriminant Foo_I is a convenient way to convert X
       --  to a Foo.Ref. The compiler transorms all references to Foo_I
       --  into references to the selector itself, in this case X.

       Val : Integer := Foo.Func (Y);
       --  Dispatching call
    end Client;

A conversion can also be made from an object of the class-wide interface reference type to an implementing reference type, by selecting the `Self` field (which is of type `java.lang.Object.Typ'Class`), and then applying a downward tagged type conversion (assuming that T derives directly or indirectly from `java.lang.Object`). Such a downward conversion will involve a run-time check, to ensure that the source object belongs to the target type's class. The package spec below illustrates one such downward conversion.

    with Foo;
    with java.lang.Object;
    package Zar is
       type Typ (Foo_I : Foo.Ref) is new java.lang.Object.Typ with record
          Field : Integer;
       end record;

       type Ref is access all Typ'Class;

       procedure Proc (This : access Typ; Val : Integer);
       function  Func (This : access Typ) return Integer;

       X : Zar.Ref := new Zar.Typ (null);
       Y : Foo.Ref := X.Foo_I;

       Z : Zar.Ref := Zar.Ref (Y.Self);
       --  OK, downward conversion, run-time check that Y designates an
       --  object in Zar.Obj'Class.
       --  Again the compiler ignores the special discriminant Self and
       --  returns the selector itself, in this case Y.
    end Zar;

In both of the cases shown above, the compiler recognizes the special idiom of selecting the interface or `Self` discriminant as meaning a reference to the object itself, reinterpreting the type of the object appropriately.

The above mechanism can also be used within another `Java_Interface` type as illustrated by the following example:

    with java.lang.Object;
    package Zoo is
       type Typ (Self : access java.lang.Object.Typ'Class) is
         new abstract java.lang.Object.Typ with null record;
       pragma Java_Interface (Typ);

       type Ref is access all Typ'Class;

       procedure Interface_Op (This : access Typ) is abstract;
    private
       pragma Convention (Java, Typ);
    end Zoo;

    with java.lang.Object; use java.lang.Object;
    with Foo;
    with Zoo;
    package Woo is
       type Typ (Foo_I : Foo.Ref;
                 Zoo_I : Zoo.Ref)
         is new abstract java.lang.Object.Typ with null record;
       pragma Java_Interface (Typ);

       type Ref is access all Typ'Class;

       --  Woo must list all of the abstract operations of interfaces
       --  Foo and Zoo.

       procedure Proc (This : access Typ; Val : Integer) is abstract;
       function  Func (This : access Typ) return Integer is abstract;
       procedure Interface_Op (This : access Typ) is abstract;

       procedure New_Op (This : access Typ) is abstract;
       --  A new operation of the interface
    private
       pragma Convention (Java, Typ);
    end Woo;

Another interesting example is the declaration of a type `Bar.Child.Typ` that derives from `Bar.Typ` and implements interface `Woo.Typ`, as shown below:

    with Foo;
    with Woo;
    package Bar.Child is
       type Typ (Foo_I : Foo.Ref;
                 Woo_I : Woo.ref)
         is new Bar.Typ (Foo_I) with null record;
       --  Note how Foo_I is used to constrain Bar.Typ. This is just to
       --  satisfy Ada semantics requirements and has no other implications.

       type Ref is access all Typ'Class;

       procedure Proc (This : access Typ; Val : Integer);
       function  Func (This : access Typ) return Integer;
       procedure Interface_Op (This : access Typ);
       procedure New_Op (This : access Typ);
    end Woo;

An interesting point to note is when an Ada tagged type `Deriv` derives from an Ada tagged type `Base` which implements a number of interfaces. If `Deriv` does not implement any additional interface there is no need to specify interface discriminants for `Deriv`, since it can simply inherit those of `Base`.

[ Next: Pragma Import Java | Previous: Using Java Interfaces | Up: Java-Specific Pragmas ]

## The `Java_Constructor` Pragma

- Background on Java Constructors:

- Using Java Constructors in Ada:

- Java Constructors and Ada Allocators:

[ Next: Using Java Constructors in Ada | Previous: The Java_Constructor Pragma | Up: The Java_Constructor Pragma ]

### Background on Java Constructors

A Java constructor is a special method that must be invoked immediately after allocating an object, in order to initialize the object. Given the following Java class:

    public class C {
       public int field;
       public C ()      { field = 3; }
       public C (int i) { field = i; }
    }

then the statement `C obj = new C (3)` accomplishes two things:

1. It allocates a new instance of class `C` in the Java heap and sets `obj` to point to this object;
2. It then calls the constructor that takes an `int` parameter, passing `obj` to it as a hidden parameter and the value 3 for its `int` parameter.

If no constructor is provided, as in the following class:

    class D extends C {
       float f;
    }

then a default constructor

    public D () {
       super ();
    }

is automatically generated for class `D`. The call of `super()` inside this default constructor (known as a no-arg constructor) invokes the no-arg constructor of the superclass of `D`, that is, the constructor of class `C`.

Generally speaking, the first statement of every constructor must either be a call to another constructor of the class, or a call to a constructor of the superclass. For instance, given a constructor

    public C (int i, int j) { this (i + j); }

The call `this (...)` invokes another constructor in the same class whose profile matches the parameters specified in `(...)`. As another example, consider:

    public D (int k) { super (k); }

where again `super (...)` invokes a constructor in the superclass whose profile matches the parameters specified in `(...)`.

The observant reader will note that in both of the original constructors of class C, there are no calls to either `this (...)` or `super (...)`. When no such call is explicitly given, the Java compiler automatically inserts calls to the no-arg constructor in the superclass. If the superclass does not have a no-arg constructor (more on this below), then you must explicitly insert calls to `super (...)` or `this (...)`.

As noted above, a class might not have a no-arg constructor. This can occur only when explicit constructors are defined in the class. In this case, the no-arg constructor is not automatically generated for the class, and if a no-arg constructor is desired, you must add it yourself. For instance, in the following class:

    public class A {
       int ival;
       public A (int i) { ival = i; }
    }

    public class B extends A {
       float fval;
       public B (float f) { fval = f; }
    }

the Java compiler will issue a compile-time error reporting that no constructor matching `A ()` was found in class `A`, because the compiler tries to insert such a call at the beginning of `B`. To correct this problem the Java programmer must either add a no-arg constructor `A ()` in class `A`, or else change the definition of `B`'s constructor to contain an explicit constructor, e.g., as follows:

    public B (float f) {
      super (0);
      fval = f;
    }

[ Next: Java Constructors and Ada Allocators | Previous: Background on Java Constructors | Up: The Java_Constructor Pragma ]

### Using Java Constructors in Ada

To assert that an Ada function function-name should be mapped to a Java constructor of some Ada tagged-type, we have introduced the `Java_Constructor` pragma. Its syntax is as follows:

    pragma Java_Constructor (function-name);

where function-name is the name of a function declared immediately within the same declarative part where the pragma occurs, and the function must have the following characteristics:

1. The function's result type must be an access type designating a class-wide type declared at the same declarative level as the function (`access tagged-type'Class`);
2. The last function parameter should be named `This`, its type must be a named access type designating tagged-type`'Class`, and it should have a `null` default value;
3. The very first declaration in the function body should contain an object declaration with a default initial expression of the form `constructor-func (..., This)`, where the constructor-func is a `Java_Constructor` function which belongs either to tagged-type or to the parent type of tagged-type;

The effect of a `Java_Constructor` pragma is to compile function-name into a constructor for the class corresponding to tagged-type. In addition, whenever function-name is invoked with a `null` value for parameter `This`, the compiler calls the `tagged-type` object allocator and passes in the pointer to the newly allocated object in lieu of the value `null`.

A `Java_Constructor` pragma is a program unit pragma. It can appear in the same places where an `Inline` pragma for function-name can appear. The `Java_Constructor` pragma applies to all the overloaded function-name subprograms declared immediately within the declarative region containing the pragma.

As an example, the following Java code:

    public class C {
       public int field;
       public C ()             { field = 3; }
       public C (int i)        { field = i; }
       public C (int i, int j) { this (i + j); }
    }

is equivalent to the following Ada:

    with java.lang.Object;  --  more on this package in the coming sections
    use  java.lang.Object;
    package C is
       use java.lang;

       type Typ is new java.lang.Object.Typ with record
          Field : Integer;
       end record;

       type Ref is access all Typ'Class;

       function new_C (This : Ref := null) return Ref;
       function new_C (I : Integer; This : Ref := null) return Ref;
       function new_C (I, J : Integer; This : Ref := null) return Ref;

    private
       pragma Java_Constructor (new_C);
    end C;

    package body C is
       function new_C (This : Ref := null) return Ref is
          Super : Object.Ref := Object.new_Object (Object.Ref (This));
       begin
          This.Field := 3;
          return This;
       end new_C;

       function new_C (I : Integer; This : Ref := null) return Ref is
          Super : Object.Ref := Object.new_Object (Object.Ref (This));
       begin
          This.Field := I;
          return This;
       end new_C;

       function new_C (I, J : Integer; This : Ref := null) return Ref is
          Ignore : Ref := new_C (I + J, This);
       begin
          return This;
       end new_C;
    end C;

[ Previous: Using Java Constructors in Ada | Up: The Java_Constructor Pragma ]

### Java Constructors and Ada Allocators

An interesting question raised by the `Java_Constructor` pragma is the interaction between Ada allocators and constructors. For instance a client of package `C` given in the previous section could write:

    with C;
    procedure Client is
       Obj_1 : C.Ref := new_C;
       Obj_2 : C.Ref := new C.Typ;  -- what happens here ???

What JGNAT does in the allocator case is to call the no-arg constructor if present (in the example `new_C (This : Ref := null)`). If there is no no-arg constructor then an error is emitted by the JGNAT compiler (this last check is currently not yet supported, and there will be an exception at run time).

[ Next: Pragma Export Java | Previous: The Java_Constructor Pragma | Up: Java-Specific Pragmas ]

## Pragma Import Java

For convention Java, pragma `Import` has the following syntax:

    pragma Import ([Convention    =>] Java,
                   [Entity        =>] Local_Name
                 [,[External_Name =>] String_Expression]);

where Local_Name is the name of an object, subprogram, record component, exception, or package, while String_Expression is a string giving the Java name of the imported entity. If String_Expression is missing it is taken to be the Local_Name, all in lower-case letters.

- Importing Packages:

- Importing Exceptions:

- Importing Record Components:

- Importing Dispatching Subprograms:

- Importing Objects:

- Importing Non-Dispatching Subprograms:

[ Next: Importing Exceptions | Previous: Pragma Import Java | Up: Pragma Import Java ]

### Importing Packages

If the Local_Name of an `Import` pragma is the name of a package spec P, then all the entities declared in P must be explicitly imported from Java. The String_Expression of such an `Import` pragma gives the name of the Java class corresponding to P and can be a simple class name or it can have the form java_package_name`.`class_name, which indicates that the class class_name corresponding to P belongs to Java package java_package_name. If java_package_name is missing, the class belongs to the anonymous Java package.

The precise rules when importing a package P are:

- All the entities declared inside P must be imported either by means of the `Import` pragma or by using other Java-specific pragmas.
- P should contain at most one tagged or untagged record type whose name must be `Typ`. `Typ` models the record part of the class corresponding to P.
- P can contain at most one exception, whose `Import` pragma must have exactly the same String_Expression as for P. (In `jvm2ada` such an exception is present only if the class corresponing to P derives, directly or indirectly, from class `java.lang.Throwable`. The name we have selected for such an exception is `Except`.)
- P should not contain task types or protected types.
- The String_Expression of the `Import` pragma for an object, subprogram, or record component declared in P must be a simple name (it cannot contain any "`.`" characters).
- If P contains nested packages, these must themselves contain an `Import` pragma (and the above rules apply recursively).

As a first example consider the following package:

    with java.lang.Object; --  more on this package in the coming sections
    package root.outer.Child is
       type Typ is new java.lang.Object.Typ with record
          x : Integer;
          pragma Import (Java, x, "x");

          Y : Integer;
          pragma Import (Java, Y, "Y");
       end record;

       type Ref is access all Typ'Class;

       procedure Dispatching_Op (This : access Typ; I : Integer);
       function Non_Dispatching_Op (F : Float) return Integer;

       function New_Child (This : Ref := null) return Ref;
       Global : Integer;

    private
       pragma Import (Java, Dispatching_Op, "someProcedure");
       pragma Import (Java, Non_Dispatching_Op, "someFunction");
       pragma Java_Constructor (New_Child);
       pragma Import (Java, Global);
    end root.outer.Child;
    pragma Import (Java, Outer.Child, "root.outer.CHILD");

This package imports into Ada the services of a class whose spec in Java looks like:

    package root.outer;
    public class CHILD extends java.lang.Object {
       public int x;
       public int Y;

       public void someProcedure (int i);
       public static int someFunction (float f);

       public CHILD ();

       public static int global;
    }

Note that in the Ada spec, the Java methods `someProcedure` and `someFunction` have been named `Dispatching_Op` and `Non_Dispatching_Op`.

[ Next: Importing Record Components | Previous: Importing Packages | Up: Pragma Import Java ]

### Importing Exceptions

If the Local_Name of an `Import` pragma is the name of an exception E, the String_Expression of such an `Import` pragma gives the name of the JVM class corresponding to E and can be a simple class name or it can have the form java_package_name`.`class_name which says that the JVM class class_name corresponding to E belongs to Java package java_package_name. If java_package_name is missing, the JVM class belongs to the anonymous Java package.

When importing an exception you should make sure that the imported JVM class is indeed a Java exception, i.e. it derives from `java.lang.Throwable`.

As an example here is an excerpt of the spec of class `java.lang.Throwable` generated by `jvm2ada`:

    package java.lang.Throwable is
       type Typ ...;
       type Ref is access all Typ'Class;

       Except : Exception;
       ...
    private
       pragma Import (Java, Except, "java.lang.Throwable);
       ...
    end java.lang.Throwable;
    pragma Import (Java, java.lang.Throwable, "java.lang.Throwable");

[ Next: Importing Dispatching Subprograms | Previous: Importing Exceptions | Up: Pragma Import Java ]

### Importing Record Components

If the Local_Name of an `Import` pragma is the name of a record field, then the record field must be declared in a record whose convention is Java and the record must be declared in a package specification which is itself imported. In this case String_Expression must be a simple name (i.e. contains no dots) giving the name of the imported field.

[ Next: Importing Objects | Previous: Importing Record Components | Up: Pragma Import Java ]

### Importing Dispatching Subprograms

If the Local_Name of an `Import` pragma is the name of a dispatching subprogram (i.e., a primitive operation of a tagged type), then the subprogram must be declared in a package specification which is itself imported. In this case String_Expression must be a simple name (i.e. contains no dots) giving the name of the imported subprogram.

[ Next: Importing Non-Dispatching Subprograms | Previous: Importing Dispatching Subprograms | Up: Pragma Import Java ]

### Importing Objects

If the Local_Name of an `Import` pragma is the name of an object and the object is declared in a package specification which is itself imported the String_Expression must be a simple name (i.e. contains no dots) giving the name of the imported Java static field.

An `Import` pragma for an object can be given even though such an entity does not occur in a package spec with an `Import` pragma. In this case the String_Expression of the `Import` pragma must give the complete Java name of the imported as shown in the following example:

    procedure Foo is
       Var : Integer;
       pragma Import (Java, Var, "pack.Foo.the_var");
    begin
       Var := 3;
    end Foo;

[ Previous: Importing Objects | Up: Pragma Import Java ]

### Importing Non-Dispatching Subprograms

If the Local_Name of an `Import` pragma is the name of a non-dispatching subprogram and the subprogram is declared in a package specification which is itself imported the String_Expression must be a simple name (i.e. contains no dots) giving the name of the imported Java static method.

An `Import` pragma for a non-dispatching subprogram can be given even though such an entity does not occur in a package spec with an `Import` pragma. In this case the String_Expression of the `Import` pragma must give the complete Java name of the imported as shown in the following example:

    procedure Foo is
       X : Integer;
       function Compute (I : Integer) return Integer;
       pragma Import (Java, Compute, "pack.Bar.calc");
    begin
       X := Compute (3);
    end Foo;

[ Previous: Pragma Import Java | Up: Java-Specific Pragmas ]

## Pragma Export Java

In the absence of pragma `Export`, the name of any Ada object, field, or subprogram compiled into a class file is the name of the corresponding Ada entity in lower-case letters.

For exceptions, record types and packages, the names of the generated class files are all in lower case.

By using pragma `Export` the user can change the default name that is generated by the JGNAT compiler. In addition, for Ada packages it can also specify which Java package they belong to. For convention Java, the pragma `Export` has the following syntax:

    pragma Export ([Convention    =>] Java,
                   [Entity        =>] Local_Name
                 [,[External_Name =>] String_Expression]);

where Local_Name is the name of an object, subprogram, record component, record type, exception, or package, and String_Expression is a string giving the Java name of the exported entity. If String_Expression is missing it is taken to be the Local_Name, all in lower-case letters.

- Exporting Objects Subprograms and Record Components:

- Exporting Exceptions:

- Exporting Packages or Record Types:

[ Next: Exporting Exceptions | Previous: Pragma Export Java | Up: Pragma Export Java ]

### Exporting Objects, Subprograms, and Record Components

NOTE: Exporting of record components is not yet supported.

If the Local_Name of an `Export` pragma is the name of an object, record component, or subprogram (but not a top-level subprogram), String_Expression must be a simple name (i.e., it contains no `.` characters), giving the name of the corresponding entity at the JVM level. As an example, when compiling the following package specification:

    package C is
       type Typ is tagged record
          Field : Integer;
          pragma Export(Java, Field, "THE_FIELD");
       end record;

       function Instance_Op (This : access Typ; I : Integer) return Integer;

       Var : Integer;
       function Op (J : Integer) return Integer;

    private
       pragma Export (Java, Instance_Op, "dispatch_op");
       pragma Export (Java, Var, "the_var");
    end C;

this is interpreted as the following two class specification at the JVM level:

    public class c {
       public static int the_var;
       public static int op (int j);
    }
    public class c$typ {
       public int THE_FIELD;
       public int dispatch_op (int i) {...}
    }

Note that when exporting an object, subprogram, or record component you cannot specify its JVM class, as this is determined by the compiler.

[ Next: Exporting Packages or Record Types | Previous: Exporting Objects Subprograms and Record Components | Up: Pragma Export Java ]

### Exporting Exceptions

If the Local_Name of an `Export` pragma is the name of an exception E, then the String_Expression of such an `Export` pragma gives the name of the generated JVM class for the Ada exception, overriding the name that would have been given by the compiler. String_Expression can be a simple class name, or it can have the form

    java_package_name.class_name

indicating that the generated class belongs to Java package java_package_name. If the name java_package_name is missing, the class is defined to belong to the anonymous Java package.

Care must be taken not to use the same class name for two Ada exceptions, packages or record types when they belong to different source files located in the same directory, since one `.class` file would overwrite the other.

[ Previous: Exporting Exceptions | Up: Pragma Export Java ]

### Exporting Packages or Record Types

NOTE: Exporting of packages is not yet supported.

If the Local_Name of an `Export` pragma is the name of a package spec or record type P, then the String_Expression of such an `Export` pragma gives the name of the generated JVM class, overriding the name that would have been given by the compiler. String_Expression can be a simple class name, or it can have the form java_package_name`.`class_name indicating that the generated JVM class belongs to Java package java_package_name. If java_package_name is missing, the JVM class belongs to the anonymous Java package.

Care must be taken not to use the same class name for two Ada exceptions, packages or record types when they belong to different source files located in the same directory, since one `.class` file would overwrite the other.

If the same `Export` pragma is specified for a package spec and a record type contained inside it, then the JGNAT compiler will map both of these in the same JVM class. For instance without `Export` pragmas the following code generates 2 JVM `.class` files: `outer$child.class` and `outer$child$rec.class`.

    package Outer.Child is
       type Rec is tagged record
         F : Float;
       end record;
       procedure Proc (This : Rec);
       --  This always goes in the same .class file as type Rec

       function Global (I : Integer) return Rec;
       --  This always goes in the same .class file as the package
    end Outer.Child;

If the same `Export` pragma is used a single class file is generated (`CHILD.class` in JVM package `root.outer`).

    package Outer.Child is
       type Rec is record
         X : Float;
       end record;
       pragma Export (Java, Rec, "root.outer.CHILD");

       procedure Proc (This : Rec);
       function Global (I : Integer) return Rec;
       --  Both subprograms are generated in the same .class file
    end Outer.Child;
    pragma Export (Java, Outer.Child, "root.outer.CHILD");

[ Next: Creating Gnapplets with JGNAT | Previous: Java-Specific Pragmas | Up: (dir) ]

# Mapping Java into Ada

This chapter details the mapping used by `jvm2ada` to map Java `.class` files into Ada package specs. It is assumed that the reader is familiar with the Java language.

- Identifiers:

- Scalar Types:

- Java References and java.lang.Object:

- Array Types:

- The Ada Package Java:

- Use of With-Type Clauses by jvm2ada:

- Java Packages:

- Java Classes:

- Abstract Classes:

- Final Classes and Final Methods:

- Nested Classes:

- Java Interface:

- Java Class Implementing Interfaces:

- Java Exceptions:

- Static Fields:

- Final Static Fields:

- Instance Fields:

- Volatile and Transient Fields:

- Static Methods:

- Instance Methods:

- Abstract Methods:

- Native Methods:

- Visibility Issues:

- Java Implicit Upcasting in Ada:

- Mixing Ada Strings and Java Strings:

- An Example:

[ Next: Scalar Types | Previous: Mapping Java into Ada | Up: Mapping Java into Ada ]

## Identifiers

See [Identifier Mangling].

[ Next: Java References and java.lang.Object | Previous: Identifiers | Up: Mapping Java into Ada ]

## Scalar Types

Java scalar tpes are mapped into Ada scalar types as follows:

              boolean (1 byte)  maps into Standard.Boolean
              char    (2 bytes)  "    "   Standard.Wide_Character

              byte    (1 byte)   "    "   Standard.Short_Short_Integer
              short   (2 bytes)  "    "   Standard.Short_Integer
              int     (4 bytes)  "    "   Standard.Integer
              long    (8 bytes)  "    "   Standard.Long_Integer

              float   (4 bytes)  "    "   Standard.Float
              double  (8 bytes)  "    "   Standard.Long_Float

As a convenience for the Ada programmer subtypes are used to express the correspondence between primitive numeric Java types and the Ada scalar types defined in package `Standard`.

We have chosen to place these subtypes at the root of the Ada version of the Java API, i.e., in package `Java`. Thus these subtypes are directly available in the Ada version of the API and at hand for users of the API. The code excerpt below gives the beginning of package `java`:

    package java is
       pragma Preelaborate;

       subtype boolean is Standard.Boolean;
       subtype char    is Standard.Wide_Character;
       subtype byte    is Standard.Short_Short_Integer;
       subtype short   is Standard.Short_Integer;
       subtype int     is Standard.Integer;
       subtype long    is Standard.Long_Integer;
       subtype float   is Standard.Float;
       subtype double  is Standard.Long_Float;
       ...
    end java;

[ Next: Array Types | Previous: Scalar Types | Up: Mapping Java into Ada ]

## Java References and `java.lang.Object`

When it comes to composite objects such as arrays and records, Java differs from Ada in the fact that it only has reference semantics. More precisely, in Java you can only allocate an object in the garbage-collected heap and obtain a reference to such object. All object reads and writes are done via this reference. In addition, you cannot copy an object as a whole into another object: there is no default deep-copy operation in Java.

In mapping Java services to Ada, we have preserved its reference semantics, as shown in the code excerpt below which shows the salient part of how class `java.lang.Object` is mapped into Ada:

    package java.lang.Object is
       pragma Preelaborate;

       type Typ is tagged limited private;
       type Ref is access all Typ'Class;

       function new_Object (This : Ref := null) return Ref;
       --  The constructor
       ...
    private

       type Typ is tagged limited null record;
       ...
    end java.lang.Object;

As a first remark, tagged types imported from Java should be limited since, as mentioned before, no object assignment operation exists on the JVM. Second, unlike Java, in Ada we need to define two types: one for the actual tagged type (type `Typ`) and one for the actual refernces (type `Ref`). This means that while in Java you can write something like:

    import java.lang.Object;
    class client {
       void foo () {
          Object obj = new Object ();
       }
    }

in Ada you have to write:

    with java.lang.Object; use java.lang.Object;
    procedure Foo is
       obj : Object.Ref = new_Object;
    begin
       null;
    end Foo;

Furthermore, for now we impose some restrictions on types that extend types that are declared in packages imported from Java.

Since the parent type of such a type extension has convention Java, the extended type inherits convention Java (even though declared within a normal Ada package). This means that the extended type should not contain any component declarations that would not be appropriate in an equivalent Java class.

In particular, a type that extends from a Java-convention parent type should not have any components of the following kinds:

- components with default initialization (excepting access components that are initialized by null)
- components of composite types (arrays, records, tasks, protected types)
- components of private types whose full type is a composite type

The reason for these restrictions is that each of the above formsu of components requires some kind of run-time initialization at the time an object of the containing type is created. Such initialization needs to happen before any user code can reference the components. However, in the presence of user-defined constructors, which are executed immediately after object creation (as required by the JVM), this is difficult for the compiler to support.

The workaround for cases where composite components are desired is instead to declare components of access types that designate the types you want to use. The allocation and initialization of those access components can then be performed as part of the actions of your own user-defined constructor function (see [The Java_Constructor Pragma]).

If we were to allow such components, the consequences of failing to heed the above restrictions would include the creation of objects that are not fully allocated or initialized, with the potential for crashing the program.

The JGNAT compiler will reject the attempt to declare a Java-convention record type with any of the restricted forms of components by flagging each offending component. We plan to try relaxing these restrictions in a future release of JGNAT.

[ Next: The Ada Package Java | Previous: Java References and java.lang.Object | Up: Mapping Java into Ada ]

## Array Types

Let's illustrate the mapping with an example. Assume you would like to map a Java array of `int` into Ada. For instance, in Java you might write:

    int[] obj;
    //  obj is a reference to an array of int

    obj = new int [3];
    //  Allocate an array-of-int object with 3 elements.
    //  The index of the first element is zero.

The above is mapped into the following Ada declarations:

    type int_Arr_Obj is array (Natural range <>) of int;
    type int_Arr     is access all int_Arr_Obj;

    obj : int_Arr;
    --  int[] obj;

    obj := new int_Array_Obj (0 .. 2);
    --  obj = new int [3];

Java does not have multidimensional arrays, it only has arrays of arrays. As a result

    int[][] obj2 = new int [3][2];

is mapped into

    type int_Arr_2_Obj is array (Natural range <>) of int_Arr;
    type int_Arr_2     is access all int_Arr_2_Obj;

    Obj2 : int_Arr_2 := new int_Arr_2_Obj (0 .. 2, 0 .. 1);
    --  obj2 = new int [3][2];

The final question that remains to answer is where are the various array type definitions located. Scalar array types have been placed in package `Java`, while array types associated with a given JVM class are placed in the Ada package spec for that class. Indeed when processing a JVM class C, `jvm2ada` generates the following at the beginning of the Ada package spec coresponding to C:

    package C is
       pragma Preelaborate;

       type Typ is ...;
       type Ref is access all Typ'Class;

       type Arr_Obj is array (Natural range <>) of Ref;
       type Arr     is access all Arr_Obj;

       type Arr_2_Obj is array (Natural range <>) of Arr;
       type Arr_2     is access all Arr_2_Obj;

       ...
    end C;

[ Next: Use of With-Type Clauses by jvm2ada | Previous: Array Types | Up: Mapping Java into Ada ]

## The Ada Package `Java`

    package java is
       pragma Preelaborate;

       subtype boolean is Standard.Boolean;
       subtype char    is Standard.Wide_Character;
       subtype byte    is Standard.Short_Short_Integer;
       subtype short   is Standard.Short_Integer;
       subtype int     is Standard.Integer;
       subtype long    is Standard.Long_Integer;
       subtype float   is Standard.Float;
       subtype double  is Standard.Long_Float;

       --  boolean array types: boolean [], boolean [][], boolean [][][]

       type boolean_Arr_Obj   is array (Natural range <>) of boolean;
       type boolean_Arr       is access all boolean_Arr_Obj;

       type boolean_Arr_2_Obj is array (Natural range <>) of boolean_Arr;
       type boolean_Arr_2     is access all boolean_Arr_2_Obj;

       type boolean_Arr_3_Obj is array (Natural range <>) of boolean_Arr_2;
       type boolean_Arr_3     is access all boolean_Arr_3_Obj;

       --  char array types: char [], char [][], char [][][]

       type char_Arr_Obj   is array (Natural range <>) of char;
       type char_Arr       is access all char_Arr_Obj;

       type char_Arr_2_Obj is array (Natural range <>) of char_Arr;
       type char_Arr_2     is access all char_Arr_2_Obj;

       type char_Arr_3_Obj is array (Natural range <>) of char_Arr_2;
       type char_Arr_3     is access all char_Arr_3_Obj;

       --  byte array types: byte [], byte [][], byte [][][]

       type byte_Arr_Obj   is array (Natural range <>) of byte;
       type byte_Arr       is access all byte_Arr_Obj;

       type byte_Arr_2_Obj is array (Natural range <>) of byte_Arr;
       type byte_Arr_2     is access all byte_Arr_2_Obj;

       type byte_Arr_3_Obj is array (Natural range <>) of byte_Arr_2;
       type byte_Arr_3     is access all byte_Arr_3_Obj;

       --  short array types: short [], short [][], short [][][]

       type short_Arr_Obj   is array (Natural range <>) of short;
       type short_Arr       is access all short_Arr_Obj;

       type short_Arr_2_Obj is array (Natural range <>) of short_Arr;
       type short_Arr_2     is access all short_Arr_2_Obj;

       type short_Arr_3_Obj is array (Natural range <>) of short_Arr_2;
       type short_Arr_3     is access all short_Arr_3_Obj;

       --  int array types: int [], int [][], int [][][]

       type int_Arr_Obj   is array (Natural range <>) of int;
       type int_Arr       is access all int_Arr_Obj;

       type int_Arr_2_Obj is array (Natural range <>) of int_Arr;
       type int_Arr_2     is access all int_Arr_2_Obj;

       type int_Arr_3_Obj is array (Natural range <>) of int_Arr_2;
       type int_Arr_3     is access all int_Arr_3_Obj;

       --  long array types: long [], long [][], long [][][]

       type long_Arr_Obj   is array (Natural range <>) of long;
       type long_Arr       is access all long_Arr_Obj;

       type long_Arr_2_Obj is array (Natural range <>) of long_Arr;
       type long_Arr_2     is access all long_Arr_2_Obj;

       type long_Arr_3_Obj is array (Natural range <>) of long_Arr_2;
       type long_Arr_3     is access all long_Arr_3_Obj;

       --  float array types: float [], float [][], float [][][]

       type float_Arr_Obj   is array (Natural range <>) of float;
       type float_Arr       is access all float_Arr_Obj;

       type float_Arr_2_Obj is array (Natural range <>) of float_Arr;
       type float_Arr_2     is access all float_Arr_2_Obj;

       type float_Arr_3_Obj is array (Natural range <>) of float_Arr_2;
       type float_Arr_3     is access all float_Arr_3_Obj;

       --  double array types: double [], double [][], double [][][]

       type double_Arr_Obj   is array (Natural range <>) of double;
       type double_Arr       is access all double_Arr_Obj;

       type double_Arr_2_Obj is array (Natural range <>) of double_Arr;
       type double_Arr_2     is access all double_Arr_2_Obj;

       type double_Arr_3_Obj is array (Natural range <>) of double_Arr_2;
       type double_Arr_3     is access all double_Arr_3_Obj;

    end java;

[ Next: Java Packages | Previous: The Ada Package Java | Up: Mapping Java into Ada ]

## Use of With-Type Clauses by `jvm2ada`

Consider the following

    public class C extends B implements I {
       public D link;
       ...
    }

When `jvm2ada` is invoked to process `C.class` to create an Ada spec for `C`, it is difficult to know whether reference type `D` is involved in a circular dependency with class `C`. First of all, `D.class` may not even be available yet. Even if it were, classes `C` and `D` could be involved in a complex circular relationship with other classes, some of which may not be available. In addition, in the presence of circular dependencies there is no good reason for using a `with type` clause in one package spec and a regular `with` clause in another.

There are three cases in which a class `C` refers to another class X:

1. `C` extends X.
2. `C` implements X.
3. X is used as a reference (e.g., a reference to an object or array of objects of type X).

In the first case, the Ada package spec corresponding to `C` needs to have a regular `with` clause for the package spec corresponding to X. In all other cases a `with type` clause suffices.

As a result, `jvm2ada` will generate the following `with` and `with type` clauses for the class `C` above:

    with B;
    with type I.Ref is access;
    with type D.Ref is access;

[ Next: Java Classes | Previous: Use of With-Type Clauses by jvm2ada | Up: Mapping Java into Ada ]

## Java Packages

A Java package pack is mapped into an empty Ada package spec pack. For instance, Java package `java.lang` is mapped into the following Ada spec:

    package java.lang is
       pragma Preelaborate;
    end java.lang;

[ Next: Abstract Classes | Previous: Java Packages | Up: Mapping Java into Ada ]

## Java Classes

A Java class X.Y.D extending a class W.Z.B is mapped into an Ada package X.Y.D containing a tagged type definition `Typ` that extends W.Z.B`.Typ` and a reference type definition `Ref` as shown below:

    pragma Extensions_Allowed (On);
    --  This pragma is generated to allow use of these packages without
    --  forcing the user to apply the -gnatX switch, which would normally
    --  be required since
    --  with type clauses are generated for this package.

    with Java; use Java;

    package X.Y.D is
       pragma Preelaborate;

       -----------------------
       -- Type Declarations --
       -----------------------

       type Typ;
       type Ref is access all Typ'Class;

       --  Array type declarations for X.Y.D

       type Arr_Obj is array (Natural range <>) of Ref;
       type Arr     is access all Arr_Obj;

       type Arr_2_Obj is array (Natural range <>) of Arr;
       type Arr_2     is access all Arr_2_Obj;

       type Arr_3_Obj is array (Natural range <>) of Arr_2;
       type Arr_3     is access all Arr_3_Obj;

       --  The actual type declaration for X.Y.D

       type Typ is new W.Z.B.Typ
          with record

             ------------------------
             -- Field Declarations --
             ------------------------
             ...
          end record;

       ------------------------------
       -- Constructor Declarations --
       ------------------------------
       ...

       -------------------------
       -- Method Declarations --
       -------------------------
       ...

       ---------------------------
       -- Variable Declarations --
       ---------------------------
       ...

    private
       pragma Convention (Java, Typ);
       ...  --  other pragmas are generated here
    end X.Y.D;
    pragma Import (Java, X.Y.D, "W.Z.B");
    pragma Extensions_Allowed (Off);

In addition, all of the static variables of X.Y.D are mapped into variables of the Ada package and all static methods of X.Y.D are mapped into nondispatching subprograms in the Ada package.

Each instance method of class X.Y.D is converted into a primitive operation of type X.Y.D`.Typ` whose first parameter is of type "`access Typ`" and whose remaining parameters are as in the Java class.

Constructors in class X.Y.D are mapped into subprograms in package X.Y.D as described in a previous section (see [The Java_Constructor Pragma]).

[ Next: Nested Classes | Previous: Java Classes | Up: Mapping Java into Ada ]

## Abstract Classes

Java's abstract classes are exactly equivalent to Ada's abstract tagged types and are mapped into such types by `jvm2ada`.

[ Next: Java Interface | Previous: Abstract Classes | Up: Mapping Java into Ada ]

## Nested Classes

A class `Inner` nested inside a class `Outer` is mapped into a child package named
`Outer.Inner`.

[ Next: Java Class Implementing Interfaces | Previous: Nested Classes | Up: Mapping Java into Ada ]

## Java Interface

See [Creating Java Interfaces with Pragma Java_Interface].

[ Next: Java Exceptions | Previous: Java Interface | Up: Mapping Java into Ada ]

## Java Class Implementing Interfaces

See [Using Java Interfaces].

[ Next: Static Fields | Previous: Java Class Implementing Interfaces | Up: Mapping Java into Ada ]

## Java Exceptions

When processing a JVM class, `jvm2ada` must figure out whether this class is a Java exception, i.e. whether it derives, directly or indirectly from class `java.lang.Throwable`.

To determine this, `jvm2ada` traverses the inheritance tree and must locate the `.class` files of the ancestor classes (see [Class File Search Paths]). If the class is indeed a Java exception, an Ada exception is added to the generated Ada spec as shown in the following example:

    package pack1.pack2;
    public class C extends java.lang.Throwable { ... }

is mapped into

    package pack1.pack2.C is
       ...
       Except : Exception;
       ...
    end pack1.pack2.C;

[ Next: Final Static Fields | Previous: Java Exceptions | Up: Mapping Java into Ada ]

## Static Fields

A static field in Java is equivalent to a regular variable in Ada and is mapped accordingly by `jvm2ada`.

[ Next: Instance Fields | Previous: Static Fields | Up: Mapping Java into Ada ]

## Final Static Fields

A Java `final` static field is equivalent to an Ada constant. When importing a final static field from Java, `jvm2ada` maps each such field to an Ada deferred constant with an associated pragma `Import` Java.

[ Next: Volatile and Transient Fields | Previous: Final Static Fields | Up: Mapping Java into Ada ]

## Instance Fields

An instance field is mapped by `jvm2ada` into a field of its corresponding tagged type.

[ Next: Static Methods | Previous: Instance Fields | Up: Mapping Java into Ada ]

## Volatile and Transient Fields

The JVM `volatile` and `transient` attributes are currently ignored by `jvm2ada`.

[ Next: Instance Methods | Previous: Volatile and Transient Fields | Up: Mapping Java into Ada ]

## Static Methods

A Java static method is equivalent to a regular nondispatching subprogram in Ada and is mapped that way by `jvm2ada`.

[ Next: Abstract Methods | Previous: Static Methods | Up: Mapping Java into Ada ]

## Instance Methods

Each instance method is converted into a primitive operation whose first parameter is of type "`access Typ`" and whose remaining parameters are as given for the Java method.

[ Next: Native Methods | Previous: Instance Methods | Up: Mapping Java into Ada ]

## Abstract Methods

Java's abstract methods are exactly equivalent to Ada's abstract primitive operations and are mapped accordingly by `jvm2ada`.

[ Next: Final Classes and Final Methods | Previous: Abstract Methods | Up: Mapping Java into Ada ]

## Native Methods

In Java one can assert that a certain method is `native`, i.e., that its implementation is provided in some native language such as C or Ada, external to the JVM. The `jvm2ada` tool ignores the `native` attribute when mapping JVM methods into Ada, since JVM methods are invoked in exactly the same way regardless of whether they have a `native` attribute.

[ Next: Visibility Issues | Previous: Native Methods | Up: Mapping Java into Ada ]

## Final Classes and Final Methods

Java has a way to restrict further derivation from a class type or further overriding of a primitive operation. For instance, given

    public class Base { ... }
    public final class Deriv extends Base { ... }

it is possible to create subclasses of `Base` but not of `Deriv`, since `Deriv` is marked `final`. Likewise, given

    public class Base {
       public       int service_1 () { ... }
       public final int service_2 () { ... }
    }

it is possible to override method `service_1` in every subclass of `Base`, whereas `service_2` cannot be overriden.

Limiting type derivation and primitive operation overriding is not directly possible in Ada. We have therefore chosen for the time being to ignore `final` classes and methods (a comment is emitted before them but nothing more). If a Java final class is extended or a final method overridden in Ada, an exception (or verifier error) will be emitted at execution time.

[ Next: Java Implicit Upcasting in Ada | Previous: Final Classes and Final Methods | Up: Mapping Java into Ada ]

## Visibility Issues

- A `public` Java class is mapped into a public Ada package spec.
- A non-public Java class containing `public` nested classes is mapped into an empty Ada package (much in the same way Java packages are mapped into Ada packages). This ensures that the parent Ada package is defined for the child classes.
- A `public` Java member is mapped into an entity declared in the public part of the corresponding Ada package if all of its parameter and return types refer to a public Java class.
- A `protected` Java member is mapped into an entity declared in the public part of the corresponding Ada package and treated like a `public` Java member as described in the above bullet point. Because in Ada there is no concept similar to the `protected` qualifier in Java, if you use a protected entity from Ada in a way that is forbidden by the JVM a run-time exception will occur.
- A `private` Java member corresponds to an Ada entity declared in a package body. `jvm2ada` ignores all such entities.
- Java entities declared as non-public (i.e. with no Java access qualifiers) are visible only to Java classes belonging to the same Java package and are intended to be accessed only from classes in the same API as `C`. `jvm2ada` ignores all such entities.

[ Next: Mixing Ada Strings and Java Strings | Previous: Visibility Issues | Up: Mapping Java into Ada ]

## Java Implicit Upcasting in Ada

Given the following two class definitions:

    public class Base {
       public static void proc (Base p, Base q) {...}
    }
    public class Derived extends Base {...}

Java allows the following code to be written (and Java programmers take advantage of the following):

    Base    obj1 = new Base ();
    Derived obj2 = new Derived ();
    proc (obj1, obj2);

The implicit conversion from the pointer to the `Derived` type to the `Base` type is completely safe and is allowed in Java much as Ada allows implicit conversion between similar anonymous access types (in Java when you write "`Derived obj2`" you are really saying that `obj2` is a pointer to an object of type `Derived` whose pointer type is anonymous). If `jvm2ada` mapped class Base into:

    package Base is
       type Typ;
       type Ref is access all Typ'class;
       ...
       procedure proc (P1 : Base.Ref; P2 : Base.Ref);
       ...
    end Base;

The call to `proc` in Ada would have to look like

       obj1 : Base.Ref    := new_Base;
       obj2 : Derived.Ref := new_Derived;
       proc (obj1, Base.Ref (obj2));

which is verbose (especially when using real class names) without any fundamental reason (writing "`proc (obj1, obj2.all'access)`" would hardly be any terser). To address this inconvenience we have used access parameters when generating the Ada equivalent to `proc`:

    procedure proc (P1 : access Base.Typ'Class;
                    P2 : access Base.Typ'Class);

allowing us to write:

       obj1 : Base.Ref    := new_Base;
       obj2 : Derived.Ref := new_Derived;
       proc (obj1, obj2);

The observant reader will notice that this new mapping into Ada of procedure `proc` is not equivalent to the first one since in the case of access parameters Ada checks that the parameters are not `null` (and an exception will be raised if they are).

This problem is worked around by disabling the `null` access check in package specs imported from Java. Note that this is a temporary expedient until a solution to this problem is agreed upon by the ISO WG9-sponsored Ada Rapporteur Group (ARG).

[ Next: An Example | Previous: Java Implicit Upcasting in Ada | Up: Mapping Java into Ada ]

## Mixing Ada Strings and Java Strings

To facilitate the use of regular Ada strings in Java routines we have added the following type definition and subprograms to the body of package `java.lang.String` generated by `jvm2ada`:

    ---------------------------------------------------
    -- Java String to Ada String Conversion Routines --
    ---------------------------------------------------

    type String_Access is access all Standard.String;
    function "+" (S : java.lang.String.Ref) return String_Access;
    function "+" (S : Standard.String) return java.lang.String.Ref;

With the above you can write:

    procedure P (JS : java.lang.String.Ref);
    function  F return java.lang.String.Ref;

    S_Ptr String_Access := +F;
    P (+"hello JGNAT");

[ Previous: Mixing Ada Strings and Java Strings | Up: Mapping Java into Ada ]

## An Example

As an example consider the following Java class

    package A.B;

    public class Foo
      extends    java.awt.event.ComponentAdapter
      implements java.io.Serializable
    {
       //  Instance Variables

       public int   i_Field;
       public float f_Filed;

       //  Constructors

       public Foo () {}
       public Foo (java.lang.String s) {}

       //  Instance Methods

       public void first_op  (java.lang.Thread t) {}
       public int  second_op () {return 1;}

       //  Static Variables

       public static int   i_Var;
       public static float f_Var;

       //  Static Methods

       public static void proc  (Foo obj, int [] b) {}
       public static int  funct (Foo [][] a, int l, int h) {return 1;}
    }

After processing this class using the following `jvm2ada` command (java-dir is the location of Sun's JDK 1.2 installation):

    jvm2ada -Ljava-dir/jdk1.2.2/jre/lib/rt.jar Foo.class

we obtain the following Ada spec (comments in italics have been added for explanatory purposes):

    pragma Extensions_Allowed (On);
    with Java; use Java;
    with java.awt.event.ComponentAdapter;
    with type java.awt.event.ComponentListener.Ref is access;
    with type java.io.Serializable.Ref is access;
    with type java.lang.String.Typ is tagged;
    with type java.lang.Thread.Typ is tagged;

    package A.B.Foo is
       pragma Preelaborate;

       -----------------------
       -- Type Declarations --
       -----------------------

       type Typ;
       type Ref is access all Typ'Class;

       type Arr_Obj is array (Natural range <>) of Ref;
       type Arr     is access all Arr_Obj;

       type Arr_2_Obj is array (Natural range <>) of Arr;
       type Arr_2     is access all Arr_2_Obj;

       type Arr_3_Obj is array (Natural range <>) of Arr_2;
       type Arr_3     is access all Arr_3_Obj;

       type Typ
          (ComponentListener_I : java.awt.event.ComponentListener.Ref;
          --  In the Ada mapping all implemented interfaces must appear
          --  in the list of discriminants. The discriminats corresponding
          --  to those inherited from the parent type (in this case
          --  Component_Listener) must be used to constrain the parent
          --  type in the Ada tagged type definition.
          Serializable_I : java.io.Serializable.Ref)
          is new
             java.awt.event.ComponentAdapter.Typ (ComponentListener_I)
          with record

             ------------------------
             -- Field Declarations --
             ------------------------

             i_Field : java.Int;
             pragma Import (Java, i_Field, "i_Field");

             f_Filed : java.Float;
             pragma Import (Java, f_Filed, "f_Filed");

          end record;

       ------------------------------
       -- Constructor Declarations --
       ------------------------------

       function new_Foo (This : Ref := null)
                         return Ref;

       function new_Foo (P1 : access java.lang.String.Typ'Class;
                         This : Ref := null)
                         return Ref;

       -------------------------
       -- Method Declarations --
       -------------------------

       procedure first_op (This : access Typ;
                           P1 : access java.lang.Thread.Typ'Class);

       function funct (P1 : A.B.Foo.Arr_2;
                       P2 : java.Int;
                       P3 : java.Int)
                       return java.Int;

       procedure proc (P1 : access A.B.Foo.Typ'Class;
                       P2 : java.Int_Arr);

       function second_op (This : access Typ)
                           return java.Int;

       ---------------------------
       -- Variable Declarations --
       ---------------------------

       i_Var : Java.Int;
       f_Var : Java.Float;

    private

       pragma Convention (Java, Typ);
       pragma Java_Constructor (new_Foo);
       pragma Import (Java, first_op, "first_op");
       pragma Import (Java, funct, "funct");
       pragma Import (Java, proc, "proc");
       pragma Import (Java, second_op, "second_op");
       pragma Import (Java, i_Var, "i_Var");
       pragma Import (Java, f_Var, "f_Var");

    end A.B.Foo;
    pragma Import (Java, A.B.Foo, "A.B.Foo");
    pragma Extensions_Allowed (Off);

The following code shows you how to use `Foo`'s services in your code.

    with java.lang.String; use java.lang.String;
    with A.B.Foo; use A.B.Foo;
    use Java;

    procedure Client is
       O  : Foo.Ref   := new_Foo (+"hello there");
       AO : Foo.Arr_2 :=
          new Foo.Arr_2_Obj
            (0 .. 9 =>
               new Foo.Arr_Obj (0 .. 3 => new_Foo));
       I  : int       := funct (A, A'Last, 7);
       AI : Java.Int_Arr := new Java.Int_Arr_Obj (0 .. 5);
    begin
       proc (O, AI);
    end Client;

[ Next: Debugging Ada Programs | Previous: Mapping Java into Ada | Up: (dir) ]

# Creating Gnapplets with JGNAT

This chapter explains how you can use JGNAT to create a "gnapplet" (GNAT applet).

- Extending java.applet.Applet.Typ:

- Initializing and Finalizing the JGNAT Runtime:

- Compiling the Gnapplet:

- Creating the HTML file:

The examples provided with your JGNAT installation contain a couple of gnapplet examples. This chapter explains the steps that you need to take to create your own gnapplets.

[ Next: Initializing and Finalizing the JGNAT Runtime | Previous: Creating Gnapplets with JGNAT | Up: Creating Gnapplets with JGNAT ]

## Extending `java.applet.Applet.Typ`

The first thing you need to do to create an applet is to extend `java.Applet.Applet.Typ` as shown in the followng example:

    with java; use java;
    with java.applet.Applet;
    with java.awt.Graphics;

    package Animate is
       --  Typ implements the same interfaces as Applet.Typ and no
       --  new interfaces, so we do not need to add discriminants to the
       --  type definition below.

       type Typ is new java.applet.Applet.Typ with record
          Count : Integer;
       end record;
       type Ref is access all Typ'Class;

       procedure Init    (This : access Typ);
       procedure Start   (This : access Typ);
       procedure Stop    (This : access Typ);
       procedure Destroy (This : access Typ);

    private
       pragma Convention (Java, Typ);
    end Animate;

In addition to extending `java.applet.Applet.Typ`, some functions from
`java.applet.Applet` need to be overridden, namely:

       procedure Init (This : access Typ);
       --  This function is called the first time the JVM initializes the
       --  the applet. This is where you should put your own initializations
       --  as well as the call to the elaboration code for the Ada runtime
       --  library, as shown in the next section.

       procedure Start (This : access Typ):
       procedure Stop  (This : access Typ);
       --  These routines are called when your applet starts or stops
       --  running (e.g., when it becomes visible to the user,
       --  or when the user moves to another page)

       procedure Destroy (This : access Typ);
       --  Called by the browser or applet viewer to inform this applet
       --  that it is being reclaimed and that it should destroy any
       --  resources that it has allocated. The stop method will always
       --  be called before destroy.
       --  A subclass of Applet should override this method if it has
       --  any operation that it wants to perform before it is destroyed.

In addition you may want to override the following two methods:

      procedure Paint (This     : access Typ;
                       Graphics : access Java.Awt.Graphics.Typ'Class);
      --  Called every time the applet needs to be repainted.
      --  Every drawing should be done on Graphics. See the Java API
      --  documentation for more info.

      procedure Update (This : access Typ;
                        G    : access java.awt.Graphics.Typ'Class);
      --  The AWT calls this method in response to a call to
      --  repaintupdate or paint. See the Java API
      --  documentation for more info.

[ Next: Compiling the Gnapplet | Previous: Extending java.applet.Applet.Typ | Up: Creating Gnapplets with JGNAT ]

## Initializing and Finalizing the JGNAT Runtime

When writing the code for your gnapplet you must remeber to initialize the JGNAT runtime upon startup of your applet. You must also remember to finalize the JGNAT runtime upon destruction of your applet. This is easy to do: you just need to call the routine `Adainit` in method `Init` and the routine `Adafinal` in method `Destroy`. As usual `Adainit` and `Adafinal` have been generated by `jgnatbind` if switch `-n` is selected.

The only additional thing you need to know is the name of the class file where `jgnatbind` generates these routines. The name of this class file is `ada_`gnapplet-name, where gnapplet-name is the name of the gnapplet package where `java.applet.Applet.Typ` was derived.

As an example here is the body of methods `Init` and `Destroy` of the `Animate` gnapplet example given in the previous section:

    package body Animate is
       ...
       procedure Init (This : access Typ) is
          procedure Adainit;
          pragma Import (Ada, Adainit, "ada_animate.adainit");
       begin
          Adainit;
          --  other initializations go here, after the call to Adainit
       end Init;

       procedure Destroy (This : access Typ) is
          procedure Adafinal;
          pragma Import (Ada, Adafinal, "ada_animate.adafinal");
       begin
          --  other finalizations go here, before the call to Adafinal
          Adafinal;
       end Destroy;
       ...
    end Animate

[ Next: Creating the HTML file | Previous: Initializing and Finalizing the JGNAT Runtime | Up: Creating Gnapplets with JGNAT ]

## Compiling the Gnapplet

Once you have written your gnapplet, you need to compile it. This is done in the usual fashion, except for the fact that because there is no main program you need to call the binder and the linker by hand. As an example, to compile the gnapplet given in package `Animate` given in the previous example you can type:

        $ jgnatmake animate
        $ jgnatbind -n animate.ali
        $ jgnatlink animate.ali
        $ jarmake -o animate.jar animate$typ.class

The `jarmake` command is particularly important for packaging all the `.class` files needed by your gnapplet in a single zip archive.

[ Previous: Compiling the Gnapplet | Up: Creating Gnapplets with JGNAT ]

## Creating the HTML file

The last step before running your gnapplet is to create an HTML file that will be loaded into your viewer or browser. This HTML file should include a special tag that indicates where you want to run your applet, and what size its allotted window should be. The `WIDTH` and `HEIGHT` parameters below are mandatory. The `ARCHIVE` parameter is only required when you created a zip archive (as you did above with `jarmake`). As an example, a minimal html file for the previous example could be:

        <html><head></head></head>
        <body>
          <APPLET CODE="animate$typ.class"
           ARCHIVE="animate.jar"
           WIDTH=200 HEIGHT=200> </APPLET>
        </body> </html>

[ Next: Index | Previous: Creating Gnapplets with JGNAT | Up: (dir) ]

# Debugging Ada Programs

Because JGNAT generates class files that are fully compliant with Sun's JVM standard, you can use any JVM debugger, such as Sun's `jdb`, with JGNAT. As a side note, there are several graphical interfaces to `jdb`. You can use GLIDE (the GNAT IDE), or you can use DDD.

The minor drawback of using a JVM debugger directly is that for those Ada constructs that are not directly available in the Java programming language (e.g. attributes), you need to know how JGNAT compiles these into bytecode in order to retrieve their value.

The purpose of this chapter is precisely to explain how the JGNAT compiler compiles Ada contructs into bytecode so that you can use any Java debugger on your Ada application.

Note that this chapter is not yet complete. If you need to understand what the JGNAT compiler generates for a particular Ada construct which is not documented below, we suggest running the command `jvmlist -g` on the generated JVM `.class` files.

- Ada Compilation Units and JVM Class Files:

- Lexical Elements:

- Enumeration Types:

- Integer Types:

- Floating Point Types:

[ Next: Lexical Elements | Previous: Debugging Ada Programs | Up: Debugging Ada Programs ]

## Ada Compilation Units and JVM Class Files

Unless pragma `Export` is used (see [Pragma Export Java]), lower-case letters are used for the names of all JVM class files generated from the compilation of an Ada unit. Likewise, the names of all of the entities generated inside a class file are lower-case.

The compilation of a nongeneric Ada library unit P always generates a JVM class file (`p.class`). In addition to the class file `p.class`, separate class files are emitted for each nested exception, record type, and tagged type declared in unit P. More specifically:

- A subprogram library unit `P` is compiled into a JVM class file `p.class` containing all the objects and nondispatching operations defined inside `P`.
- The specification and body of a library package `P` are compiled into a single JVM class file `p.class` containing all of the objects and nondispatching operations defined in the spec or body of `P`.
- Any tagged or untagged record type `R` declared inside a package or subprogram `P` is treated like a static inner class in Java, that is, a new JVM class `p$r.class` is generated containing `R`'s fields as instance variables, and, if `R` is a tagged type, its associated dispatching operations.
- A package `Q` nested inside an Ada unit `P` does not result in a separate class. Entities declared within the nested package will generally be associated as members of the containing library package's class (except in the case of exceptions or type declarations that, as usual, result in their own class). However, the names of the corresponding fields and methods resulting from the nested package will be given expanded names that include the name of the outermost library package followed by the names of any enclosing nested packages, and where adjacent pairs of simple names in the expanded are separated by dollar sign characters (e.g., `p$q$proc`).
- A child unit `P.Q` is compiled into the JVM class file `p$q.class`. All the rules described here are applied recursively with respect to `Q`'s contents.
- A generic package instantiation `R` nested inside an Ada unit `P` is treated exactly like a nested package.
- A generic subprogram instantiation `S` nested inside an Ada unit `P` treated exacly like a nested subprogram.
- An Ada exception `E` declared inside an Ada unit `P` is treated like a member class in Java and is compiled into JVM class `p$e.class`.
- A task type or protected type T nested inside an Ada unit `P` is compiled into JVM class file `p$t.class`.
- A subprogram `N` nested inside another subprogram `P` will be treated as a static method of the enclosing library unit's class and will be given an expanded name that includes the names of any enclosing subprograms (e.g., `pkg$p$n`). In addition, a special class will be generated for the nested subprogram's enclosing subprogram to contain fields for any objects of the enclosing subprogram that are referenced by the nested subprogram. The name of this special Activation Record class is constructed by appending the prefix `__AR_` to the name of the enclosing subprogram (e.g., `__AR_pkg$p`).
- Any other Ada type or construct `X` occurring inside an Ada unit `P` that needs to generate a standalone JVM class will be compiled into `p$x.class`.

As an example, the compilation of the following package:

    package Outer is
       package Nested is
          type Typ is tagged record
             Field : Integer;
          end record;

          E : exception
       end Nested;

       type Rec is record
         X : Float;
       end record;
    end Outer;

yields the following JVM class files: `outer.class`, `outer$nested$typ.class`,
`outer$nested$e.class`, `outer$rec.class`.

[ Next: Enumeration Types | Previous: Ada Compilation Units and JVM Class Files | Up: Debugging Ada Programs ]

## Lexical Elements

All Ada identifiers are mapped into the corresponding lower case identifiers when generating symbolic references for the JVM, unless `pragma Export` is used (but note that certain names corresponding to internal entities generated by the GNAT front end may inlude upper-case letters).

[ Next: Integer Types | Previous: Lexical Elements | Up: Debugging Ada Programs ]

## Enumeration Types

An Ada enumeration type is converted into a Java 1-byte, 2-byte, 4-byte or 8-byte integer whose size best matches the value of the largest enumeration literal.

Character types are treated like regular Ada enumeration types. More specifically, an Ada `Character` type is mapped into a Java `byte`, whereas an Ada `Wide_Character` type is mapped onto the equivalent 2-byte Java `char` type.

An Ada boolean type is treated like a standard Ada enumeration type with 2 values and is consequently mapped into a Java `byte`.

[ Next: Floating Point Types | Previous: Enumeration Types | Up: Debugging Ada Programs ]

## Integer Types

Each signed integer type is mapped into the smallest corresponding JVM integer type whose size is able to represent all required integer values:

          Short_Short_Integer  is mapped into  byte  (1 byte)
          Short_Integer         "    "     "   short (2 bytes)
          Integer               "    "     "   int   (4 bytes)
          Long_Integer          "    "     "   long  (8 bytes)
          Long_Long_Integer     "    "     "   long  (8 bytes)

Each modular type is also mapped into the smallest corresponding Java integer type whose size is able to represent all required modular values.

[ Previous: Integer Types | Up: Debugging Ada Programs ]

## Floating Point Types

The Ada predefined floating point types map very naturally onto Java's IEEE 32-bit float and IEEE 64-bit double:

          Short_Float     is mapped into  float  (4 bytes)
          Float            "    "     "   float  (4 bytes)
          Long_Float       "    "     "   double (8 bytes)
          Long_Long_Float  "    "     "   double (8 bytes)

User-defined floating point types are mapped into `Float` where possible, and `Long_Float` otherwise.

[ Previous: Debugging Ada Programs | Up: (dir) ]

# Index

#### Menu

- `-c` (`jvm2ada`): Switches for jvmlist
- `-I` (`jvm2ada`): Switches for jvm2ada
- `-j` (`jarmake`): Switches for jarmake
- `-k` (`jarmake`): Switches for jarmake
- `-k` (`jvm2ada`): Switches for jvm2ada
- `-L` (`jarmake`): Switches for jarmake
- `-L` (`jvm2ada`): Switches for jvm2ada
- `-n` (`jarmake`): Switches for jarmake
- `-o` (`jarmake`): Switches for jarmake
- `-o` (`jvm2ada`): Switches for jvm2ada
- `-q` (`jarmake`): Switches for jarmake
- `-q` (`jvm2ada`): Switches for jvmlist
- `-q` (`jvm2ada`): Switches for jvm2ada
- `-q` (`jvm2ada`): Switches for jvmstrip
- `-q` (`jvm2ada`): Switches for jvmlist
- `-s` (`jvm2ada`): Switches for jvm2ada
- `-v` (`jarmake`): Switches for jarmake
- `-v` (`jvm2ada`): Switches for jvm2ada
- `-w` (`jvm2ada`): Switches for jvm2ada
- Conventions: Conventions
- jarmake: Building Archives with jarmake
- jvm2ada: Using the Java API with jvm2ada
- jvmlist: Viewing Class Files with jvmlist
- jvmstrip: Stripping Debug Info with jvmstrip
- Typographical conventions: Conventions