J2ME 2D 遊戲入門之旅（四）：子彈群管理與碰撞檢測

設計目標

飛機遊戲中子彈數量大、頻繁生成銷毀，若每顆子彈對應一個 Sprite 會嚴重消耗記憶體。解決方案：共享單一 Sprite，以二維陣列管理子彈狀態。

Bullets 類別核心結構

public class Bullets extends GameObject {
    private int[][] bullets; // [index][0:type, 1:x, 2:y, 3:vx, 4:vy, 5:alive]
    private int bulletsTotal;
    private Random rnd;
    public static final int TYPE_LEFT=0, TYPE_RIGHT=1, TYPE_TOP=2, TYPE_BOTTOM=3;
    private int screenW, screenH;

    public Bullets(Image img, int pw, int ph, int total, int w, int h) {
        super(img, pw, ph);
        bulletsTotal = total;
        bullets = new int[total][6];
        rnd = new Random();
        screenW = w; screenH = h;
    }

    public void initBullets() { for(int i=0;i screenW+5) bullets[i][3] *= -1;
        if (bullets[i][2] < -5 || bullets[i][2] > screenH+5) bullets[i][4] *= -1;
    }

    public void paint(Graphics g) {
        for (int i=0; i