October 1, 2020
How to make Custom Exceptions in Java

In our previous post, we have learned about types of exceptions, throws and throw. Today we are going to make a custom-defined exception, in simple means we will create an exception according to our requirement. 

Basically, there are two types of exceptions, one is built-in exceptions and the other is User-Defined Exceptions. But today we are going to create a User-Defined Exception with a help of throw keyword. User-Defined exceptions are made to fulfill a specific purposes which sometimes built-in exception does not fulfill.

First, let us understand how to make a user-defined exception:-

  • Creating a custom exception class that will be extending an Exception class or its child classes(which is a base class for all exceptions.)
  • You can create a constructor or simple print a statement inside user-defined exception class.

Let us see a program below which will clearly explain the concept .

class MyException {
       void validAge() {
          int age=18;
          try {
              if (age<18) {
                   throw new AgeNotDefined();
               }
         }catch(AgeNotDefined e) {
               e.printStackTrace();
               System.out.println("Age is less than 18");
            }
       }
}
public class AgeNotDefined extends Exception {
       public static void main(String[] args) {
               System.out.println("UserDefinedException");
      }
}

In the above example, we thr0w an exception AgeNotDefined which is a user-defined exception and remember that for creating user-defined exceptions we have to use a throw keyword. These Exceptions can have any name but you have to define it according to your need. 

Feel free to try this example and comment below.

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