monster inheritance

Chandler-Gilbert Community College Spring 2005

Borrow a Monster class and MonsterControl class from someone else in our section of java.

Use inheritance (extends) to create a new derived Monster2 class that adds 2 new things to what the borrowed base Monster class does (2 new methods). You may do more, if you like. Here's how:

CHANGE THE MONSTER PARENT CLASS
Change your instance variables from private to protected. That way, your derived class will be able to use them. (From the perspective of object-oriented programming, it's not "proper" to use the protected keyword. Instead, you should write accessor functions for every private variable you want your derived class to use. The protected keyword is the "practical" approach. In this case, practical means quicker and easier, so we're going to do it the practical way.) This is the only change you need to make to the parent class.

CREATE THE MONSTER2 CHILD CLASS
1. Create a new file for the Monster2 class.
2. Create the new class and use the extends keyword:
3. Unfortunately, derived classes still must have their own constructors. So, what you've got to do is create Monster2 constructors to match each constructor in the Monster class. In the Monster2 constructors, you call the Monster constructors, using the super keyword as follows:
  
  As an aside, here are my Monster constructors that are called by super:
4. Now you can add new methods or override existing methods to train Monster2 to do additional things. Here's one I added:
CHANGE THE MONSTERCONTROLLER CLASS TO WORK WITH THE NEW MONSTER2 CHILD CLASS
Revise the monster controller so it works with your new derived Monster2 class instead of with the borrowed base Monster class. First, change your declaration so it refers to Monster2:

Then, change the line where you instantiate your monster to use Monster2:

In the end, you will have 3 files:

	The borrowed, base Monster class
	Your derived Monster2 class that adds new methods to the base Monster class
	A revised MonsterController class.

Special rules:

You are NOT allowed to change the other person's Monster class code in any way, with one exception: You can change any or all of the instance variables from private to protected.
To save time, you may use the methods you created for your own Monster class, as long as they differ in some way from what the other person did.

Challenge: add a new static method that counts the number of monsters created. To do this, add a counter variable to Monster2. Revise Monster2's constructors so that, after calling super(), they add 1 to the counter. Finally, create a static method which returns the number of monsters created. Add a button to your monster controller to test this method.

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