How to Implement User-Defined Exceptions in Java?

The following code example demonstrates How to Implement User-Defined Exceptions in Java.

Problem Statement

Develop an application in Java to create a user-defined exception class using the extends keyword.

Solution

In order to create a user-defined exception class in Java, you can extend the built-in Exception class or one of its subclasses. The following code shows an example of how to create and use a custom exception class using the extends keyword.

// Define a custom exception class by extending Exception
class CustomException extends Exception {
    public CustomException(String message) {
        super(message);
    }
}

// Create a class to demonstrate the custom exception
public class CustomExceptionDemo {
    public static void main(String[] args) {
        try {
            int result = divide(10, 0);
            System.out.println("Result: " + result);
        } catch (CustomException e) {
            System.out.println("Custom Exception caught: " + e.getMessage());
        }
    }

    public static int divide(int dividend, int divisor) throws CustomException {
        if (divisor == 0) {
            // Throw the custom exception when divisor is zero
            throw new CustomException("Division by zero is not allowed.");
        }
        return dividend / divisor;
    }
}

In this example:

We define a custom exception class called CustomException that extends the built-in Exception class. This custom exception class has a constructor that accepts a message as an argument.
In the CustomExceptionDemo class, we have a divide method that throws the CustomException when the divisor is zero.
In the main method, we attempt to divide by zero, which triggers the custom exception. So, we catch and handle this exception in the catch block, printing the custom error message.

This demonstrates how to create a user-defined exception class using the extends keyword and use it to handle specific exceptions in your Java application.

Problem Statement

Solution

Further Reading