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Trail: Essential Classes
Lesson: Exceptions
Section: Catching and Handling Exceptions
Exceptions
What Is an Exception?
The Catch or Specify Requirement
Catching and Handling Exceptions
The try Block
The catch Blocks
The finally Block
Putting It All Together
Specifying the Exceptions Thrown by a Method
How to Throw Exceptions
Chained Exceptions
Creating Exception Classes
Unchecked Exceptions — The Controversy
Advantages of Exceptions
Summary
Questions and Exercises
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The try Block

> The first step in constructing an exception handler is to enclose the code that might throw an exception within a `try` block. In general, a `try` block looks like the following.

> >     try {
> >         code
> >     }
> >     catch and finally blocks . . .

> The segment in the example labeled `code` contains one or more legal lines of code that could throw an exception. (The `catch` and `finally` blocks are explained in the next two subsections.)

> To construct an exception handler for the `writeList` method from the `ListOfNumbers` class, enclose the exception-throwing statements of the `writeList` method within a `try` block. There is more than one way to do this. You can put each line of code that might throw an exception within its own `try` block and provide separate exception handlers for each. Or, you can put all the `writeList` code within a single `try` block and associate multiple handlers with it. The following listing uses one `try` block for the entire method because the code in question is very short.

> >     private Vector vector;
> >     private static final int SIZE = 10;

> >     PrintWriter out = null;

> >     try {
> >         System.out.println("Entered try statement");
> >         out = new PrintWriter(new FileWriter("OutFile.txt"));
> >         for (int i = 0; i < SIZE; i++) {
> >             out.println("Value at: " + i + " = "
> >                          + vector.elementAt(i));
> >         }
> >     }
> >     catch and finally statements . . .

> If an exception occurs within the `try` block, that exception is handled by an exception handler associated with it. To associate an exception handler with a `try` block, you must put a `catch` block after it; the next section shows you how.

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