Ajax Hacks

Checked and Unchecked Exceptions

Java exceptions can be separated into two distinct groups: checked and unchecked. A checked exception signals an abnormal condition that the client must handle. All checked exceptions must either be caught and handled within the calling method or be declared in the throws clause following the method signature. This is why they are called "checked." The compiler and the JVM will verify that all checked exceptions that can occur in a method are handled. The compiler and JVM don't care if unchecked exceptions are ignored, because these are exceptions that the client usually cannot handle anyway. Unchecked exceptions, such as j ava.lang.ClassCastException, are typically the result of incorrect logic or programming errors.

The determination of whether an exception is checked or unchecked is based simply on its location in the exception hierarchy. All classes that are descendants of the java. lang.Exception class, except for subclasses of RuntimeException , are checked exceptions; the compiler will ensure that they are either handled by the method or listed in the throws clause. RuntimeException and its descendants are unchecked exceptions, and the compiler will not complain about these not being listed in a throws clause for a method or being handled in a try/catch block. This is why they are referred to as "unchecked."