The throw statement

The throw statement allows throwing any exception that a programmer deems necessary. One can even create their own exception. To create a checked exception, extend the java.lang.Exception class:

class MyCheckedException extends Exception{
    public MyCheckedException(String message){
        super(message);
    }
    //add code you need to have here
}

Also, to create an unchecked exception, extend the java.lang.RunitmeException class, as follows:

class MyUncheckedException extends RuntimeException{
    public MyUncheckedException(String message){
        super(message);
    }
    //add code you need to have here
}

Notice the comment add code you need to have here. You can add methods and properties to the custom exception as to any other regular class, but programmers rarely do it. The best practices even explicitly recommend avoiding using exceptions for driving the business logic. Exceptions should be what the name implies, covering only exceptional, very rare situations.

But if you need to announce an exceptional condition use the throw keyword and new operator to create and trigger propagation of an exception object. Here are a few examples:

throw new Exception("Something happend"); 
throw new RunitmeException("Something happened");
throw new MyCheckedException("Something happened");
throw new MyUncheckedException("Something happened");

It is even possible to throw null as follows:

throw null;

The result of the preceding statement is the same as the result of this one:

throw new NullPointerException;

In both cases, an object of an unchecked NullPointerException begins to propagate through the system, until it is caught either by the application or the JVM.