Throw new exceptions (throw keyword)

In Java, the throw keyword is used to explicitly throw an exception from a method or a block of code. It signals an error condition that must be handled or propagated up the call stack. This is different from throws, which is used in method declarations to indicate that a method can throw specific exceptions.

How to Use the throw Keyword

When you use throw, you are manually creating and throwing an exception object of a specific type. It allows you to handle specific conditions in your code where you want to signal an error. The throw statement is typically followed by an instance of a class that extends Throwable, such as Exception or RuntimeException.

Syntax:

throw new ExceptionType("Error message");

Example: Throw new Exception

Here’s a simple example of throwing an exception when a condition is not met:

public class Example {
    public static void checkAge(int age) {
        if (age < 18) {
            throw new IllegalArgumentException("Age must be 18 or older.");
        } else {
            System.out.println("Age is valid.");
        }
    }

    public static void main(String[] args) {
        try {
            checkAge(16); // This will throw an exception
        } catch (IllegalArgumentException e) {
            System.out.println("Caught Exception: " + e.getMessage());
        }
    }
}

Explanation:

• In the checkAge method, if the age is less than 18, an IllegalArgumentException is thrown with a message.
• The main method calls checkAge(16), which triggers the exception.
• The catch block catches this exception and prints the error message.