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Trail: Learning the Java Language
Lesson: Packages
Section: Creating and Using Packages
Packages
Creating and Using Packages
Creating a Package
Naming a Package
Using Package Members
Managing Source and Class Files
Summary of Creating and Using Packages
Questions and Exercises
Home Page > Learning the Java Language > Packages
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Creating a Package

> To create a package, you choose a name for the package (naming conventions are discussed in the next section) and put a `package` statement with that name at the top of every source file that contains the types (classes, interfaces, enumerations, and annotation types) that you want to include in the package.

> The package statement (for example, `package graphics;`) must be the first line in the source file. There can be only one package statement in each source file, and it applies to all types in the file.

> > Note: If you put multiple types in a single source file, only one can be `public`, and it must have the same name as the source file. For example, you can define `public class Circle` in the file `Circle.java`, define `public interface Draggable` in the file `Draggable.java`, define `public enum Day` in the file `Day.java`, and so forth.

> > You can include non-public types in the same file as a public type (this is strongly discouraged, unless the non-public types are small and closely related to the public type), but only the public type will be accessible from outside of the package. All the top-level, non-public types will be package private.

> If you put the graphics interface and classes listed in the preceding section in a package called `graphics`, you would need six source files, like this:

> >     //in the Draggable.java file
> >     package graphics;
> >     public interface Draggable {
> >         . . .
> >     }

> >     //in the Graphic.java file
> >     package graphics;
> >     public abstract class Graphic {
> >         . . .
> >     }

> >     //in the Circle.java file
> >     package graphics;
> >     public class Circle extends Graphic implements Draggable {
> >         . . .
> >     }

> >     //in the Rectangle.java file
> >     package graphics;
> >     public class Rectangle extends Graphic implements Draggable {
> >         . . .
> >     }

> >     //in the Point.java file
> >     package graphics;
> >     public class Point extends Graphic implements Draggable {
> >         . . .
> >     }

> >     //in the Line.java file
> >     package graphics;
> >     public class Line extends Graphic implements Draggable {
> >         . . .
> >     }

> If you do not use a `package` statement, your type ends up in an unnamed package. Generally speaking, an unnamed package is only for small or temporary applications or when you are just beginning the development process. Otherwise, classes and interfaces belong in named packages.

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