Tutorial Basic polymorphism example

Chalant · 11-12-2013, 08:46 AM

I was playing around trying to get the concept of polymorphism down, and I ended up creating a basic skeleton for entity-based combat (could be used in a game, though this is just barebones), simply by printing out the actions.

Main.java

Code:
package org.chaltech.project;

import org.chaltech.project.model.NPC;
import org.chaltech.project.model.Player;

/**
 * @author Chalant <chalant123@gmail.com>
 */
public class Main {
	
	/**
	 * Constructor for our main class,
	 * use this to assign object variables.
	 */
	public Main() {
		Player player = new Player("Chalant", 10);
		Player playerTwo = new Player("Nonchalant", 9);
		
		NPC npc = new NPC("Rat", 6);
		NPC npcTwo = new NPC("Goblin", 9);
		
		/**
		 * Player vs NPC
		 */
		player.attack(npc, 1);
		npc.attack(player, 2);
		
		/**
		 * NPC vs NPC
		 */
		npc.attack(npcTwo, 3);
		
		/**
		 * Player vs Player
		 */
		player.attack(playerTwo, 3);
	}
	
	/**
	 * Initialisation method, use this to invoke
	 * the constructor for our main class
	 * @param args
	 */
	public static void main(String[] args) {
		new Thread(new Runnable() {
			public void run() {
				new Main();
			}
		}).start();
	}
	
}

Entity.java

Code:
package org.chaltech.project.model;

/**
 * @author Chalant <chalant123@gmail.com>
 */
public abstract class Entity {

	public abstract void attack(Entity entity, int damage);
	
	public abstract void setHealth(int health);
	
	public abstract int getHealth();
	
	public abstract String getName();
	
}

Player.java

Code:
package org.chaltech.project.model;

/**
 * @author Chalant <chalant123@gmail.com>
 */
public class Player extends Entity {

	private int health;
	private String name;
	
	public Player(String name, int health) {
		this.name = name;
		this.health = health;
	}
	
	public void attack(Entity entity, int damage) {
		if (entity instanceof NPC || entity instanceof Player) {
			if (!((entity.getHealth() - damage) < 0)) {
				entity.setHealth(entity.getHealth() - damage);
			} else {
				entity.setHealth(0);
			}
			System.out.println(getName() + " attacks " + entity.getName() + " and deals " + damage + " damage. \n");
			System.out.println(entity.getHealth() > 0 ? entity.getName() + " now has " + entity.getHealth() + " health. \n" : entity.getName() + " has died.\n");
		}
	}

	public void setHealth(int health) {
		this.health = health;
	}

	public int getHealth() {
		return health;
	}
	
	public String getName() {
		return name;
	}
}

NPC.java

Code:
package org.chaltech.project.model;

/**
 * @author Chalant <chalant123@gmail.com>
 */
public class NPC extends Entity {

	private int health;
	private String name;
	
	public NPC(String name, int health) {
		this.name = name;
		this.health = health;
	}

	public void attack(Entity entity, int damage) {
		if (entity instanceof Player || entity instanceof NPC) {
			if (!((entity.getHealth() - damage) < 0)) {
				entity.setHealth(entity.getHealth() - damage);
			} else {
				entity.setHealth(0);
			}
			System.out.println(getName() + " attacks " + entity.getName() + " and deals " + damage + " damage. \n");
			System.out.println(entity.getHealth() > 0 ? entity.getName() + " now has " + entity.getHealth() + " health. \n" : entity.getName() + " has died.\n");
		}
	}

	public void setHealth(int health) {
		this.health = health;
	}
	
	public int getHealth() {
		return health;
	}
	
	public String getName() {
		return name;
	}

}

Output:

Code:
Chalant attacks Rat and deals 1 damage. 

Rat now has 5 health. 

Rat attacks Chalant and deals 2 damage. 

Chalant now has 8 health. 

Rat attacks Goblin and deals 3 damage. 

Goblin now has 6 health. 

Chalant attacks Nonchalant and deals 3 damage. 

Nonchalant now has 6 health.

§herlock · 07-03-2014, 02:59 PM

Great one, I have seen people don't use abstract class which is most important here.