Question
The following is some code designed by J. Hacker for a video game. There is an Alien class to represent a monster and an AlienPack class that represents a band of aliens and how much damage they can inflict:
class Alien
{
public static final int SNAKE_ALIEN = 0;
public static final int OGRE_ALIEN = 1;
public static final int MARSHMALLOW_MAN_ALIEN = 2;
public int type; // Stores one of the three above types
public int health; // 0=dead, 100=full strength
public String name;
public Alien ( int type , int health, String name)
{
this.type = type;
this.health = health;
this.name = name;
}
}
public class AlienPack
{
private Alien[] aliens;
public AlienPack (int numAliens)
{
aliens = new Alien[numAliens];
}
public void addAlien(Alien newAlien, int index)
{
aliens[index] = newAlien;
}
public Alien[] getAliens()
{
return aliens;
}
public int calculateDamage()
{
int damage = 0;
for (int i=0; i < aliens.length; i++)
{
if (aliens[i].type==Alien.SNAKE_ALIEN)
{
damage +=10; // Snake does 10 damage
}
else if (aliens[i].type==Alien.OGRE_ALIEN)
{
damage +=6; // Ogre does 6 damage
}
else if (aliens[i].type== Alien.MARSHMALLOW_MAN_ALIEN)
{
damage +=1;
// Marshmallow Man does 1 damage
}
}
return damage;
}
}
The code is not very object oriented and does not support information hiding in the Alien class. Rewrite the code so that inheritance is used to represent the different types of aliens instead of the “type” parameter. This should result in deletion of the “type” parameter. Also rewrite the Alien class to hide the instance variables and create a getDamage method for each derived class that returns the amount of damage the alien inflicts. Finally, rewrite the calculateDamage method to use getDamage and write a main method that tests the code.
Answer
public class Alien {
protected int health;
protected String name;
Alien(){
}
Alien(int health,String name)
{
this.health=health;
this.name=name;
}
}
public class MarshmallowAlien extends Alien {
private final int damage=1;
private int number;
MarshmallowAlien(int number,int health, String name)
{
super(health,name);
this.number=number;
}
int getDamage(){
return damage;
}
int calculateDamage(){
return getDamage()*number;
}
public String toString(){
return ("The Alien "+name+" with Health "+health+" caused Damage "+calculateDamage());
}
}
public class OgreAlien extends Alien{
private final int damage=6;
private int number;
OgreAlien(int number,int health, String name)
{
super(health,name);
this.number=number;
}
int getDamage(){
return damage;
}
int calculateDamage(){
return getDamage()*number;
}
public String toString(){
return ("The Alien "+name+" with Health "+health+" caused Damage "+calculateDamage());
}
}
public class SnakeAlien extends Alien {
private final int damage=10;
private int number;
SnakeAlien(int number,int health, String name)
{
super(health,name);
this.number=number;
}
int getDamage(){
return damage;
}
int calculateDamage(){
return getDamage()*number;
}
public String toString(){
return ("The Alien "+name+" with Health "+health+" caused Damage "+calculateDamage());
}
}
public class TestMethod {
public static void main(String[] args) {
SnakeAlien alien1= new SnakeAlien(50,78,"Snake");
OgreAlien alien2= new OgreAlien(22,99,"Ogre");
MarshmallowAlien alien3=new MarshmallowAlien(44,100,"Marshmallow Alien");
System.out.println(alien1.toString());
System.out.println(alien2.toString());
System.out.println(alien3.toString());
}
}
Output
The Alien Snake with Health 78 caused Damage 500
The Alien Ogre with Health 99 caused Damage 132
The Alien Marshmallow Alien with Health 100 caused Damage 44