Throwing Exceptions

The compiler knows which exceptions must be caught when a method is called because the method specifies them in its signature.

Your methods can also throw exceptions - just add the throws to your signature and list the Throwable class(es).

If your method lists any exceptions in the throws clause of the signature, your method code does not need to catch the exception.

As a beginner, this (bad) technique lets you write code to prompt for input without handling exceptions:

public static void main (String args[]) throws IOException
{

    BufferedReader keyboard =
         new BufferedReader(new InputStreamReader(System.in));
    ...
}

If your method calls another method that throws one of the exceptions listed in the signature, execution stops and the exception is thrown.

An exception is thrown up the call chain until it is caught (or your program crashes).

In other words, if the Exception isn't caught by code in your program, then it crashes.

You can create your own exceptions by extending the Exception class or one of its child classes.

Inside your code you would add a throw statement (make sure it is listed in the signature):


throw ThrowableObject;

Any time the method is called, it will need to be inside a try/catch block.

You can also put the throw inside of your own try block and catch it there.

You may write code that catches an Exception and then re-throws it.

You can explicitly print a stack trace (the call chain of executed methods) with a call to printStackTrace()