// APS101, Winter 2009: Lecture 35 (Apr. 6)
//
// Review: last time we finished our discussion of
           basic sorting algorithms - make sure you
           know these for the final exam!

// Today we will cover the basics of Exception Handling.
// exception = an error in Java.
// For example:
int[] x;
x[0] // NullPointerException
x = new int[2];
x[5] // ArrayIndexOutOfBoundsException

// these exceptions don't just appear magically - they are "thrown" somewhere!

// Throwing an Exception
throw new Exception();
throw new Exception("This message describes the problem.");

// these exceptions can also be "caught" using a try-catch block:

try {
   // execute some code that might throw an exception
} catch (Exception e) {
   // if an exception is thrown, catch it and respond to it
}

// Example:

6 / 0 // ArithmeticException 
try {
   int x = 6 / 0;
} catch (Exception e) {
   System.out.println("Cannot divide by zero!");
}
x // doesn't exist!

// let's try that again...
int x;
int y = 6;
int z = 10;
try {
   x = y / 0;
} catch (Exception e) {
   x = z;
}
x // = 10!

// now, let's use exception handling to make the Tic-Tac-Toe game more robust (error-free)
// what if the user enters a row and/or column that is too high? i.e. greater than 2. 
// right now, the program crashes due to an ArrayIndexOutOfBoundsException
// how do we handle this? (use a try-catch block to catch the exception!)

// we can also write a customized exception, throw it when the input is invalid, and
// catch it in the driver class.

// (see TTTException.java)
TTTException e = new TTTException(); // an exception is an object!
e
e.getMessage()
TTTException e = new TTTException("APS101 Exception");
e.getMessage()

// (see method setMark in TicTacToe.java for the changes we made)
// a TTTException is thrown in 3 different cases - what are they?

// (see TTTDriver.java for the changes we made)
// we added a try-catch block to handle any TTTException that is thrown by method setMark

// Also note that you can catch multiple exceptions in the try-catch block:
try {
   // try some piece of code
} catch (Exception1 e) {
   // respond to Exception1
} catch (Exception2 e) {
   // respond to Exception2
} ...