User-defined Custom Exception in Java

Inbuilt class Exception in java can be inherited to create our own exception.  

Program creating user defined Exception by extending Exception class:

// A Class that represents user-defined expception
class DemoException extends Exception
{
    public DemoException(String s)
    {
        // Call constructor of parent Exception
        super(s);
    }
}
 
// A Class that uses above MyException
public class Main
{
    public static void main(String args[])
    {
        try
        {
            // Throw an object of user defined exception
            throw new DemoException("User Defined Exception");
        }
        catch (DemoException ex)
        {
            System.out.println("Caught");
 
            // Print the message from DemoException object
            System.out.println(ex.getMessage());
        }
    }
}

Output:

Caught
User Defined Exception

Explanation of above program:

DemoException is user defined exception inheriting inbuilt Exception class. DemoException class Default constructor calls super class constructor. In main function within try a exception of DemoException type is throw using throw keyword, this exception is caught by catch clause thus executing statements inside catch clause. System.out.println(ex.getMessage()) prints the message passed by DemoException.