What is a user defined/custom exception in Java?

User-defined exceptions can be implemented by,

• defining a class to respond to an exception and
• embedding a throw statement in the try clause where the exception can occur or declaring that the method to throw the exception to invoking method where it is handled.

A new exception can be defined by deriving it from the Exception class as follows.

public class UserDefinedException extends Exception {
	public UserDefinedException() {
		super();
	}

	public UserDefinedException(String errorMessage) {
		super(errorMessage);
	}
}

The throw statement is used to signal the occurance of the exception within a try block. Often, exceptions are instantiated in the same statement in which they are thrown using the syntax.

throw new UserDefinedException ("throwing User defined Exception.")

To handle the exception within the method where it is thrown, a catch statement that handles UserDefinedException, must follow the try block. If the developer does not want to handle the exception in the method itself, the method must pass the exception using the syntax:

public myMethodName() throws UserDefinedException

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