How can we create a custom exception in Java?

JavaObject Oriented ProgrammingProgramming

Sometimes it is required to develop meaningful exceptions based on the application requirements. We can create our own exceptions by extending Exception class in Java

User-defined exceptions in Java are also known as Custom Exceptions.

Steps to create a Custom Exception with an Example

  • CustomException class is the custom exception class this class is extending Exception class.
  • Create one local variable message to store the exception message locally in the class object.
  • We are passing a string argument to the constructor of the custom exception object. The constructor set the argument string to the private string message.
  • toString() method is used to print out the exception message.
  • We are simply throwing a CustomException using one try-catch block in the main method and observe how the string is passed while creating a custom exception. Inside the catch block, we are printing out the message.

Example

class CustomException extends Exception {
   String message;
   CustomException(String str) {
      message = str;
   }
   public String toString() {
      return ("Custom Exception Occurred : " + message);
   }
}
public class MainException {
   public static void main(String args[]) {
      try {
         throw new CustomException("This is a custom message");
      } catch(CustomException e) {
         System.out.println(e);
      }
   }
}

Output

Custom Exception Occurred : This is a custom message
raja
Published on 30-May-2019 15:17:36
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