Exceptions - Beginning Java - page 377

1. Write a program that generates exceptions of type NullPointerException , NegativeArraySizeEx-
ception , and IndexOutOfBoundsException . Record the catching of each exception by displaying the
message stored in the exception object and the stack trace record.
2. Add an exception class to the last example that differentiates between the index-out-of-bounds error
possibilities, rethrows an appropriate object of this exception class in divide() , and handles the excep-
tion in main() .
3. Write a program that calls a method that throws an exception of type ArithmeticException at a ran-
dom iteration in a for loop. Catch the exception in the method and pass the iteration count when the ex-
ception occurred to the calling method by using an object of an exception class you define.
4. Add a finally block to the method in the previous example to output the iteration count when the
method exits.

• WHAT YOU LEARNED IN THIS CHAPTER

TOPIC CONCEPT
ExceptionsExceptions identify abnormal errors that arise in your program. Exceptions are objects of subclasses of the
Throwable class.

Standard
Exceptions

Java includes a set of standard exceptions that may be thrown automatically, as a result of errors in your
code, or may be thrown by methods in the standard classes in Java.

Uncaught
Exceptions

If a method throws exceptions that aren't caught, and aren't represented by subclasses of the Error class or
the RuntimeException class, then you must identify the exception classes in a throws clause in the meth-
od definition.

Catching
Exceptions

If you want to handle an exception in a method, you must place the code that may generate the exception in
a try block. A method may have several try blocks.

Exception handling code is placed in a catch block that immediately follows the try block that contains
the code that can throw the exception. A try block can have multiple catch blocks that each deals with a
different type of exception.

catch
Blocks

A finally block is used to contain code that must be executed after the execution of a try block, regard-
less of how the try block execution ends. A finally block is always executed before execution of the
method ends.

finally
Blocks

Throwing
Exceptions

You can throw an exception by using a throw statement. You can throw an exception anywhere in a meth-
od. You can also rethrow an existing exception in a catch block to pass it to the calling method.

Defining
Exceptions

You can define your own exception classes. In general, your exceptions classes should be derived from the
Exception class to ensure that they are checked exceptions. The compiler ensures that all checked excep-
tions are dealt with in the code where such exceptions may be thrown.

Chained
Exceptions

When you throw a new exception in a catch block, you can record the previous exception by creating your
exception object to store a reference to the previous exception or by calling initCause() for your new ex-
ception object.