Java User Defined Exceptions

Java allows us to make our own exceptions called as User Defined Exceptions.

Java’s built-in exceptions handle most common errors,you will probably want to create your own exception types to handle situations specific to your applications.

How to make user defined exception?

Steps

1. Define an empty class which extends Exception class.
2. Define parameterised constructor in it and pass argument to super class.
3. Write try block which throws Exception of newly created class by using className.
4. Write catch block for UserDefined class and create object of it.
5. Print message of class using objectName.getMessage() method (optional).

Example

Program for throwing an IncorrectPasswordException when user enters a wrong password.

import java.lang.Exception //optinal
class IncorrectPasswordException extends Exception // user defined class
{
	public IncorrectPasswordException(String msg) {
	super(msg);
	}
}

public class Test 
{
	public static void main(String[] args) 
	{
		int pass=1122;
		try
		{
			if(pass != 1234)
				throw new IncorrectPasswordException("Wrong password entered");
			else
				System.out.println("Welcome user.");
		}
		catch(IncorrectPasswordException e)
		{
			System.out.println("Error! "+e.getMessage());
		}
	}
}

Output

In above example, We have created IncorrectPasswordException class which is having Exception as Parent class. We have passed the msg String in its parameterized constructor for initialization of String. In class Test we have written try block which checks for the exception based on written condition.

If condition is true then compiler will throw an IncorrectPasswordException by passing message and call the matching catch block.

User Defined Exceptions based on type of application

We can throw any exception like these.