We'll now see firsthand the benefits of using an OOP approach in games, by adding a new type of shot -
a "cluster bomb". The player will have a limited number of these bombs (for example, initially 5) and
each time he shoots one, eight fireballs will appear and dart in eight different directions. We will use
the following graphics, which in reality come from a single image rotated, flipped and mirrored as necessary:
bombUL.gif
bombU.gif
bombUR.gif
bombL.gif
bombR.gif
bombDL.gif
bombD.gif
bombDR.gif
The fireball has its own class, called Bomb, with the following source:
Bomb.java
1 /**
2 * Curso B?sico de desarrollo de Juegos en Java - Invaders
3 *
4 * (c) 2004 Planetalia S.L. - Todos los derechos reservados. Prohibida su reproducci?n
5 *
6 * http://www.planetalia.com
7 *
8 */
9 package version19;
10
11
12 public class Bomb extends Actor {
13 public static final int UP_LEFT = 0;
14 public static final int UP = 1;
15 public static final int UP_RIGHT = 2;
16 public static final int LEFT = 3;
17 public static final int RIGHT = 4;
18 public static final int DOWN_LEFT = 5;
19 public static final int DOWN = 6;
20 public static final int DOWN_RIGHT = 7;
21
22 protected static final int BOMB_SPEED = 5;
23 protected int vx;
24 protected int vy;
25
26 public Bomb(Stage stage, int heading, int x, int y) {
27 super(stage);
28 this.x = x;
29 this.y = y;
30 String sprite ="";
31 switch (heading) {
32 case UP_LEFT : vx = -BOMB_SPEED; vy = -BOMB_SPEED; sprite="bombUL.gif";break;
33 case UP : vx = 0; vy = -BOMB_SPEED; sprite="bombU.gif";break;
34 case UP_RIGHT: vx = BOMB_SPEED; vy = -BOMB_SPEED; sprite="bombUR.gif";break;
35 case LEFT : vx = -BOMB_SPEED; vy = 0; sprite = "bombL.gif";break;
36 case RIGHT : vx = BOMB_SPEED; vy = 0; sprite = "bombR.gif";break;
37 case DOWN_LEFT : vx = -BOMB_SPEED; vy = BOMB_SPEED; sprite="bombDL.gif";break;
38 case DOWN : vx = 0; vy = BOMB_SPEED; sprite = "bombD.gif";break;
39 case DOWN_RIGHT : vx = BOMB_SPEED; vy = BOMB_SPEED; sprite = "bombDR.gif";break;
40 }
41 setSpriteNames( new String[] {sprite});
42 }
43
44 public void act() {
45 super.act();
46 y+=vy;
47 x+=vx;
48 if (y < 0 || y > Stage.HEIGHT || x < 0 || x > Stage.WIDTH)
49 remove();
50 }
51 }
What's new here is that the visual aspect of the actor changes depending on the direction of movement.
Also we can see that the act() method just moves the bomb and erases it if it reaches the
limits of the screen
The Player class must be also modified in order to handle a new key for this type of
shot (we'll use the "B" key for cluster bombs), and we must also handle the number of bombs we have left:
Player.java
1 /**
2 * Curso B?sico de desarrollo de Juegos en Java - Invaders
3 *
4 * (c) 2004 Planetalia S.L. - Todos los derechos reservados. Prohibida su reproducci?n
5 *
6 * http://www.planetalia.com
7 *
8 */
9 package version19;
10
11 import java.awt.event.KeyEvent;
12
13 public class Player extends Actor {
14 protected static final int PLAYER_SPEED = 4;
15 protected int vx;
16 protected int vy;
17 private boolean up,down,left,right;
18 private int clusterBombs;
19
20
21 public Player(Stage stage) {
22 super(stage);
23 setSpriteNames( new String[] {"nave.gif"});
24 clusterBombs = 5;
25 }
26
27 public void act() {
28 super.act();
29 x+=vx;
30 y+=vy;
31 if (x < 0 || x > Stage.WIDTH)
32 vx = -vx;
33 if (y < 0 || y > Stage.HEIGHT)
34 vy = -vy;
35 }
36
37 public int getVx() { return vx; }
38 public void setVx(int i) {vx = i; }
39 public int getVy() { return vy; }
40 public void setVy(int i) {vy = i; }
41
42
43 protected void updateSpeed() {
44 vx=0;vy=0;
45 if (down) vy = PLAYER_SPEED;
46 if (up) vy = -PLAYER_SPEED;
47 if (left) vx = -PLAYER_SPEED;
48 if (right) vx = PLAYER_SPEED;
49 }
50
51 public void keyReleased(KeyEvent e) {
52 switch (e.getKeyCode()) {
53 case KeyEvent.VK_DOWN : down = false;break;
54 case KeyEvent.VK_UP : up = false; break;
55 case KeyEvent.VK_LEFT : left = false; break;
56 case KeyEvent.VK_RIGHT : right = false;break;
57 }
58 updateSpeed();
59 }
60
61 public void keyPressed(KeyEvent e) {
62 switch (e.getKeyCode()) {
63 case KeyEvent.VK_UP : up = true; break;
64 case KeyEvent.VK_LEFT : left = true; break;
65 case KeyEvent.VK_RIGHT : right = true; break;
66 case KeyEvent.VK_DOWN : down = true;break;
67 case KeyEvent.VK_SPACE : fire(); break;
68 case KeyEvent.VK_B : fireCluster(); break;
69 }
70 updateSpeed();
71 }
72
73 public void fire() {
74 Bullet b = new Bullet(stage);
75 b.setX(x);
76 b.setY(y - b.getHeight());
77 stage.addActor(b);
78 }
79
80 public void fireCluster() {
81 if (clusterBombs == 0)
82 return;
83
84 clusterBombs--;
85 stage.addActor( new Bomb(stage, Bomb.UP_LEFT, x,y));
86 stage.addActor( new Bomb(stage, Bomb.UP,x,y));
87 stage.addActor( new Bomb(stage, Bomb.UP_RIGHT,x,y));
88 stage.addActor( new Bomb(stage, Bomb.LEFT,x,y));
89 stage.addActor( new Bomb(stage, Bomb.RIGHT,x,y));
90 stage.addActor( new Bomb(stage, Bomb.DOWN_LEFT,x,y));
91 stage.addActor( new Bomb(stage, Bomb.DOWN,x,y));
92 stage.addActor( new Bomb(stage, Bomb.DOWN_RIGHT,x,y));
93 }
94
95 }
96
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