CSC108 Tutorial #12 - Inheritance

Inheritance Relationships (class hierarchy tree)

                             Machine

                            /       \
                          /           \

                  Appliance           Computer

                   /    \             /      \ 
                  /      \           /        \
                 /        \         /          \

           WashMach      Dryer   MainFrame      PC

Stuff.java

// Machine: a machine has a power rating, and a method
//			to increase its power.
class Machine {
	public int power;		// power rating for this machine

	public Machine (int power) {
		this.power = power;
	}

	// incPower: increase power rating by 20.
	public void incPower () {
		power += 20;
	}

	// getPower: get machine's power rating.
	public int getPower () {
		return power;
	}
}

// Appliance: an appliance is a machine.
class Appliance extends Machine {
	public String name;
	public String loadSize;    // small, medium, large load

	public Appliance (String name, String loadSize, int power) {
		super (power);
		this.name = name;
		this.loadSize = loadSize;
	}

	// incLoad: increase size of load
	public void incLoad () {
		if (loadSize.equals("small"))
			loadSize = "medium";
		else if (loadSize.equals("medium"))
			loadSize = "large";
	}

	// decLoad: decrease size of load
	public void decLoad () {
		if (loadSize.equals("large"))
			loadSize = "medium";
		else if (loadSize.equals("medium"))
			loadSize = "small";
	}

	// getLoadSize: returns current size of the load.
	public String getLoadSize () {
		return loadSize;
	}
}

// Computer: a computer is a machine.
class Computer extends Machine {
	public static int num = 0;   // how many Computer objects have been
							 // created?

	public Computer (int power) {
		super (power);
		num = num + 1;
	}

	// getNum: get count of how many Computer objects have been created.
	public int getNum () {
		return num;
	}
}

// WashMach: a washing machine is an appliance.
class WashMach extends Appliance {
	public WashMach (String name, String loadSize, int power) {
		super (name, loadSize, power);
	}
}

// Dryer: a dryer is an appliance.
class Dryer extends Appliance {
	public static int num = 0;   // how many Dryer objects have been created?

	public Dryer (String name, String loadSize, int power) {
		super (name, loadSize, power);
		num = num + 1;
	}

	// getNum: get count of how many Dryer objects have been created.
	public int getNum () {
		return num;
	}
}

// MainFrame: a main frame is a computer.
class MainFrame extends Computer {
	public int numUsers;	// how many users on this mainframe?

	public MainFrame (int users, int power) {
		super (power);
		numUsers = users;
	}

	// incUsers: add the specified number of users to the user count.
	public void incUsers (int more) {
		numUsers += more;
	}

	// getUsers: get count of users on this mainframe
	public int getUsers () {
		return numUsers;
	}
}

// PC: a personal computer is a computer.
class PC extends Computer {
	public PC (int power) {
		super (power);
	}
}

// Stuff: this is the test class used to create a bunch of different
//        stuff from the hierarchy described above.
class Stuff {
	public static void main (String[] args) {
		Appliance app;
		WashMach wash = new WashMach ("Kenmore", "small", 200);
		Dryer dry = new Dryer ("Miracle", "medium", 100);
		Dryer fluff = new Dryer ("GE", "small", 100);

		System.out.println ("wash " + wash.getLoadSize());
		System.out.println ("dry " + dry.getLoadSize());

		app = wash;
		app.incPower();
		wash.incPower();
		wash.incLoad();
		dry.decLoad();

		System.out.println ("wash " + wash.getLoadSize());
		System.out.println ("dry " + dry.getLoadSize());
		System.out.println ("wash " + wash.getPower());

		MainFrame dec = new MainFrame (30, 300);
		PC acer = new PC (200);
		PC ibm  = new PC (200);

		acer.incPower();
		acer.incPower();
		dec.incUsers (25);

		System.out.println();
		System.out.println ("acer " + acer.getPower());
		System.out.println ("ibm "  + ibm.getPower());
		System.out.println ("dec "  + dec.getPower());
		System.out.println ("dec users "  + dec.getUsers());

		System.out.println();
		System.out.println ("Number of Computers " + dec.getNum());
		System.out.println ("Number of Dryers    " + dry.getNum());
	}
}

Output for Stuff.java

wash small
dry medium
wash medium
dry small
wash 240

acer 240
ibm 200
dec 300
dec users 55

Number of Computers 3
Number of Dryers    2