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Home Interviews Throwing exceptions and custom exceptions explain with example in Java. – MindStick
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1 Answers

ICSM Computer
ICSM Computer 24 Apr 2025
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1. Throwing Exceptions in Java

In Java, you can throw exceptions using the throw keyword.

Syntax:

throw new ExceptionType("Error Message");

Example:

public class ThrowExample {
    public static void checkPersonAge(int age) {
        if (age < 16) {
            throw new IllegalArgumentException("Age must be 16 or above of a person");
        } else {
            System.out.println("Access granted");
        }
    }

    public static void main(String[] args) {
        checkPersonAge(16);  // This will throw an exception
    }
}

2. Custom Exceptions in Java

You can create your own exceptions by extending Exception (checked) or RuntimeException (unchecked).

Example of Custom Exception:

// Step 1: Create a custom exception
class InvalidAgeException extends Exception {
    public InvalidAgeException(String message) {
        super(message);
    }
}

// Step 2: Use the custom exception
public class CustomExceptionExample {
    public static void validatePersonAge(int age) throws InvalidAgeException {
        if (age < 16) {
            throw new InvalidAgeException("You must be at least 16 years old for person.");
        }
        System.out.println("Age is valid");
    }

    public static void main(String[] args) {
        try {
            validatePersonAge(15);  // This will throw InvalidAgeException
        } catch (InvalidAgeException e) {
            System.out.println("Caught Exception: " + e.getMessage());
        }
    }
}

Summary:

Feature Explanation
throw Used to explicitly throw an exception
throws Declares that a method can throw exceptions
Custom Exception User-defined exception for specific errors
extends Exception For checked exceptions
extends RuntimeException For unchecked exceptions
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