How to create a Custom Exception in Java

Points To Remember

• All the custom Exceptions must implement the Exception class or any of its subclass.
• There are four types of Constructors that you can use while defining your Custom Exception.

Ex 1 : Basic Custom Exception

In this case we will just created a Custom Exception where we define a Custom Exception and throw it with a message. This message is visible in the stacktrace.

class CustomException extends Exception {

 public CustomException(String message) {
  super(message);
 }

}

public class Test {
 public static void main(String args[]) {
  try {
   throw new CustomException("Throwing Custom Exception");
  } catch (CustomException e) {
   e.printStackTrace();
  }
  try {
   throw new CustomException(" ThrowingAnother Custom Exception");
  } catch (CustomException e) {
   e.printStackTrace();
  }
 }

}

The output of the above example is

CustomException: Throwing Custom Exception
at Test.main(Test.java:12)
CustomException: ThrowingAnother Custom Exception
at Test.main(Test.java:17)

Ex 2 : Custom Exception with same Message

Suppose we have a Custom Exception and we know that it will occur only because of a particular reason that we can throw the Exception without the Constructor Parameter like the following.

class CustomException extends Exception {

 public CustomException() {
  super("Custom Exception has Occured");
 }

}

public class Test {
 public static void main(String args[]) {
  try {
   throw new CustomException();
  } catch (CustomException e) {
   e.printStackTrace();
  }
  try {
   throw new CustomException();
  } catch (CustomException e) {
   e.printStackTrace();
  }
 }

}

CustomException: Custom Exception has Occured
at Test.main(Test.java:12)
CustomException: Custom Exception has Occured
at Test.main(Test.java:17)

This is a small example how you can define your own Custom Exceptions in java