J2ME 2D 遊戲開發入門（四）：子彈群管理與碰撞檢測核心算法

大量子彈的對象池復用、狀態數組驅動、半徑碰撞檢測是飛行射擊遊戲的核心模塊。本文詳細剖析 Bullets 類的完整實現。

設計核心：復用單一 Sprite 實例

數百顆子彈共享一個 Sprite 對象，通過狀態數組 記錄每顆子彈的獨立屬性：

private int[][] bullets; // [index][0:type, 1:x, 2:y, 3:vx, 4:vy, 5:alive]
private int bulletTotal; // 池大小

完整 Bullets 類實現

public class Bullets extends GameObject {
    public static final int TYPE_LEFT = 0, TYPE_RIGHT = 1, TYPE_TOP = 2, TYPE_BOTTOM = 3;
    private int[][] bullets;
    private int bulletTotal;
    private Random rnd;
    private int screenW, screenH;

    public Bullets(Image img, int fw, int fh, int total, int w, int h) {
        super(img, fw, fh); // 共享 Sprite
        this.bulletTotal = total;
        this.bullets = new int[total][6];
        this.rnd = new Random();
        this.screenW = w; this.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;
    }

    // 繪製整群 (復用 sprite)
    public void paint(Graphics g) {
        for (int i=0;i