In this section, we will learn what the throw keyword is and how it works in Java.

What does throw exception mean in Java?

So far, we’ve learned that when a program is running, if something goes wrong, the runtime will automatically produce an exception. Of course, we can handle these exceptions via `try catch` blocks.

But other than the runtime engine, we can manually produce and throw exceptions as well.

After all, exceptions are nothing but objects of a set of prebuilt classes that inherit from `Throwable` class. So when we say “throw exception” it means to create and run a new exception.

How to throw exception in Java? (Java throw Keyword Syntax)

throw ExceptionObject;

To throw an exception, we use the keyword `throw` and on the right side of this statement we put the type of exception that we want to throw.

So the combination of the keyword `throw` and the target exception object creates the exception throwing statement.

Example: throwing exception via `throw` keyword

public class Simple {

    public static void main(String[] args) {
        checkAge(16);
    }
    public static void checkAge(int age){
        try{
            if (age <18){
                throw new IllegalArgumentException("Under legal age!");
            }else{
                System.out.println("Access granted!");
            }
        }catch (IllegalArgumentException exception){
            System.out.println(exception.getMessage());
        }
    }
}

Output:

Under legal age!

Inside the body of the `checkAge()` method, we’ve run a `try` block and via the `if` statement checked to see if the input argument to the method is less than 18.

Here, because the input value is in fact less than 18, we then created a new exception (object) of type `IllegalArgumentException` and as its message we set `Under legal age! ` and throw it via the `throw` keyword.

So now a new exception is thrown and the `catch` block of this `try` block is checked to see if the type of the exception matches the type of the parameter.

Because they matched, the body of the `catch` block ran and we’ve got the message you see in the output.