AVAJAVA Web Tutorials

In JavaSW, the Exception class is a subclass of Throwable. The RuntimeException class is a subclass of Exception. If an exception is a subclass of Exception but not RuntimeException, it is a checked exception. A checked exception needs to either be caught in a method (in a try/catch block), or the method needs to specify that it can throw the exception on further (via a throws clause of a method declaration). If an exception is a subclass of RuntimeException, it is an unchecked exception. An unchecked exception can be caught, but it does not have to be. Thus, it is 'unchecked'.

An example of a typical checked exception is IOException. An example of a typical unchecked exception is a NullPointerException.

Here is an example of a checked exception class called CheckedException. It subclasses Exception. This exception class allows us to specify the exception message via a String argument to the constructor.

CheckedException.java

package test;

public class CheckedException extends Exception {
	public CheckedException(String message) {
		super(message);
	}
}

Here we can see the Type Hierarchy of CheckedException. Notice that it is a subclass of Exception, and Exception is a subclass of Throwable.

Here is a simple example of an unchecked exception class called UncheckedException. It subclasses RuntimeException. We can specify the exception message via the String argument to the constructor.

UncheckedException.java

package test;

public class UncheckedException extends RuntimeException {
	public UncheckedException(String message) {
		super(message);
	}
}

Here is the Type Hierarchy for UncheckedException. Notice that it subclasses RuntimeException.

(Continued on page 2)