In addition to simply handling Java's exceptions, you can also throw your own exception.
Here's an example of using the throw keyword.
If you are performing a calculation that might involve some division, you might wish to perform a check to see if the divisor is zero (0), and if it is, throw an exception, as in:
Notice how we must make a new instance of the appropriate class and throw that instance.
What this code does is create a method for dividing double values that throws an exception if the divisor is zero (0).
(Normally, operations involving double values never throw an exception, not even when executing something like 1.0/0.0.)
The following quiz poses questions with respect to throwing exceptions.
Throwing Exceptions - Quiz