Lecture Notes 21: Even More Working with Classes and Object-Oriented Design

Objectives

By the end of this module, you will be able to:

• Allocate, use, and pass objects as arguments.
• Use null references appropriately.
• Write classes and use objects.
• Use constructors to initialize objects.

Before Starting

If you do not have your Codio course ready, use any text editor or simple IDE. Some possibilities are:

• Write using Sublime; Compile and run in the Terminal
• Use IDEs like: IntelliJ, DrJava, or JGrasp

Zombies. Objectified Zombies. Yeeeees.

Zombies...

• Eat brains of humans.

• Turn bit humans into zombies.

• Can be killed by humans.

Humans...

• Shoot zombies in the brain (so much with the brains!).

• Fight other humans, and might kill them. (Why so mean?)

• Are turned into zombies when bit.

• Have names.

1. Make a Person class, and a ZombiesMain class. The latter has the main that will use the Person class.
2. Each Person object is either a human or a zombie.
3. If a Person object is a human, it has a name.
4. Humans can shoot Person objects.
5. Zombies can bite humans, which turns them into a zombie.
6. Person objects created with constructors with no arguments are zombies.

Person joe  = new Person("Joe");
Person bob  = new Person("Bob");
Person jane = new Person("Jane");
Person z    = new Person();

System.out.println(Person.numHumans() + " humans vs. " + Person.numZombies() + " zombies.");
z.bite(bob); // poor bob
bob.bite(z); // confused zombie
Person derpbie = bob;
derpbie.bite(derpbie); // this is getting ridiculous
System.out.println(Person.numHumans() + " humans vs. " + Person.numZombies() + " zombies.");

jane.shoot(z);    // humans FTW!
jane.shoot(joe);  // wait...what?
jane.shoot(jane); // oh...oh no.
System.out.println(Person.numHumans() + " humans vs. " + Person.numZombies() + " zombies.");

while (true) {
    derpbie.bite(derpbie); // bored zombie is bored
}

Joe, ready for action!
Bob, ready for action!
Jane, ready for action!
...mmmm, brains.  Oh noes, a zombie!
3 humans vs. 1 zombies.
Bob is gnawed on by a zombie.
The zombie formerly known as Bob bites a zombie, like an idiot.
The zombie formerly known as Bob is hungry...and remembers he has an arm.  Nomnomnomnom.
...etc...

OO Design

Why does Object-Oriented Programming (OOP) exist?

• Why is it useful? Why use OOP instead of making all code and data static?

• Come up with two examples where it has utility.

Design a set of classes and objects to describe cards for the card game "War". Write "prototype" classes that include the classes, data in the classes, and methods, but do not provide an implementation of the methods.

• What methods would you use?
• What data would each object contain?
• How would the objects be related? Which objects contain which other objects?
• How are objects initialized, and related to other objects?

• Code written for one situation should be, within reason, reusable in other situations

• Writing fairly generic classes enables this.

• It is important to design your classes before writing your code. I've been doing this for you in homeworks.

Take your design from the previous Exercise.

• How easy is it to modify it to implement the five-card-stud variant of poker?
• How about blackjack?

Redesign your objects so that many of them can be reused between games

Other factors to consider:

• We want to implement an online card game site where many people can be playing games at the same time. Do we need to more classes and relationships between objects to support multiple concurrent games?
• Take care in designing how cards move from various locations (deck, board, hand).
• Also take care in designing how decisions on who wins in the various games are made.