java - 敌人破坏 slick2d

Question

我目前正在使用 Slick2D 开发一种 Java 平台游戏，按照我当前的设置方式，敌人是 ArrayList 中的 Enemy 对象。玩家可以向他们射击小圆圈(也保存在 ArrayList 中)，如果它们连接起来，就会发生敌人“死亡”的情况。这就是我遇到麻烦的地方。我该如何摆脱这样的物体？我尝试过在 foreach 循环中将它们从数组中删除，但这会引发异常，因为它仍在搜索所述数组(我认为)。

for (Bullet bullet : bullets) {
  for (Enemy enemy : enemies) {
    if (bullet.intersects(enemy) {
      bullets.remove(bullet);
      enemies.remove(enemies);
    }
  }
}

这不起作用，所以现在我尝试创建一个子弹和敌人交互的索引数组，然后在循环后删除它们，如下所示:

for (int i = 0; i < bullets.size(); i++) {
  for (int z = 0; z < enemies.size(); z++) {
    if (bullets.get(i).intersects(enemies.get(z).getPoly())) {
      bRemove.add(i);
      eRemove.add(z);
    }
  }
}

for (Integer i : bRemove) {
  bullets.remove(i);
}

for (Integer i : eRemove) {
  enemies.remove(i);
}

现在好像什么也没发生。有谁知道我应该做什么？这是整个主类:

package ca.wmc.BasicPlatform;

import java.lang.Math;
import java.util.ArrayList;

import org.newdawn.slick.Animation;
import org.newdawn.slick.AppGameContainer;
import org.newdawn.slick.BasicGame;
import org.newdawn.slick.geom.Circle;
import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.Input;
import org.newdawn.slick.Image;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.SpriteSheet;
import org.newdawn.slick.geom.Polygon;

public class Game extends BasicGame  {

Player quote;
public BlockMap map;
private boolean start;
private int startCount;
private boolean lost;
private int lostCount;
private int hpTime = 0;
private ArrayList<Enemy> enemies;
private ArrayList<Bullet> bullets;
private int reload = 0;
private final double a = 2;
private int t = 0;

public Game() {
    super("Super Simple Platform");
}

public void init(GameContainer container) throws SlickException {
    container.setVSync(true);
    container.setTargetFrameRate(60);
    map = new BlockMap("tiled/newmap.tmx");
    quote = new Player("tiled/Quote.gif", 320, 320, 3, -8);
    enemies = new ArrayList<Enemy>();
    enemies.add(new Enemy("tiled/King.gif", 50, 0, -8, 26, 32));
    enemies.add(new Enemy("tiled/Quote.gif", 200, 150, -8, 28, 32));
    start = false;
    lost = false;
    bullets = new ArrayList<Bullet>();
}

public void update(GameContainer container, int delta) throws SlickException {
    if (!start) {
        if (container.getInput().isKeyDown(Input.KEY_Z)) {
            start = true;
        }
    } else {
        if (!lost) {

            ArrayList<Integer> eRemove = new ArrayList<Integer>();
            ArrayList<Integer> bRemove = new ArrayList<Integer>();

            quote.update(container, a, t, delta);
            for (Enemy enemy : enemies) {
                enemy.update(quote, a, t);
            }

            if (t == 5) {
                t = 0;
            } else {
                t++;
            }

            if (container.getInput().isKeyDown(Input.KEY_X) && reload == 0) {
                if (quote.getCurAnimation() == quote.right()) {
                    bullets.add(new Bullet(quote.getXPos() + 28, quote.getYPos() + (int)(20 * Math.random() - 22) + 25, "r"));
                } else {
                    bullets.add(new Bullet(quote.getXPos() + 28, quote.getYPos() + (int)(20 * Math.random() - 22) + 25, "l"));
                }
                reload = 10;
            }

            if (reload > 0) {
                reload--;
            }

            for (Bullet bullet : bullets) {
                if (bullet.getDirection()) {
                    bullet.setCenterX(bullet.getCenterX() + 10);
                } else { 
                    bullet.setCenterX(bullet.getCenterX() - 10);
                }
            }

            for (Enemy enemy : enemies) {
                if (quote.getPoly().intersects(enemy.getPoly()) && hpTime > 50 && quote.getHP() != 0) {
                    quote.setHP(quote.getHP() - 1);
                    hpTime = 0;
                    if (quote.getHP() <= 0) {
                        lost = true;
                    }
                }
            }

            hpTime++;

            if (startCount <= 100) {
                startCount++;
            }

            for (int i = 0; i < bullets.size(); i++) {
                for (int z = 0; z < enemies.size(); z++) {
                    if (bullets.get(i).intersects(enemies.get(z).getPoly())) {
                        bRemove.add(i);
                        eRemove.add(z);
                    }
                }
            }

            for (Integer i : bRemove) {
                bullets.remove(i);
            }

            for (Integer i : eRemove) {
                enemies.remove(i);
            }
        }

        if (quote.getYPos() > 640) {
            lost = true;
        }

    }
}

public void render(GameContainer container, Graphics g) throws SlickException{
    g.drawImage(new Image("apsci.jpg"), 0, 0);
    BlockMap.tmap.render(0, 0);
    g.drawAnimation(quote.getCurAnimation(), quote.getXPos(), quote.getYPos());
    for (Enemy enemy : enemies) {
        g.drawAnimation(enemy.getCurAnimation(), enemy.getXPos(), enemy.getYPos());
    }

    for (Circle bullet : bullets) {
        g.draw(bullet);
    }

    g.drawString("HP: " + quote.getHP(), 10, 450);

    if (!start) {
        g.drawString(getTitle(), 150, 0);
        g.drawString("Controls: arrow keys to move, Z to jump, X to fire.", 150, 50);
        g.drawString("Defeat the evil.          Press Z to start.", 150, 100);
    }

    if (startCount < 100) {
        for (Enemy enemy : enemies) {
            g.drawString("The Evil -->", enemy.getXPos() - 125, enemy.getYPos() + 10 + (int)(2 * Math.random()));
        }
        g.drawString("<-- You", quote.getXPos() + 50, quote.getYPos() + 10 + (int)(2 * Math.random()));
    }

    if (lost) {
        g.drawString("You have lost.", 200, 210);
    }
    if (lostCount > 150) {
        g.drawString("Game over.", 200, 260);
    }
    if (lostCount > 200) {
        g.drawString("If that wasn't already obvious.", 200, 310);
    }
}

public static void main(String[] args) throws SlickException{
    // TODO Auto-generated method stub
    try {
        AppGameContainer app = new AppGameContainer(new Game(), 640, 480, false);
        app.start();
    } catch (SlickException e) {
        e.printStackTrace();
    }

}

}

Answer 1

正如您所指出的，您无法使用 for-each 循环修改某些内容并继续迭代。相反，您需要使用迭代器:see here 。

由于在ArrayList中删除还要求被删除的对象后的每个对象左移一个索引(因此是一个O(n)操作)，我建议您可能还想考虑使用LinkedList来代替。

关于样式，您还应该始终通过其接口(interface)而不是其实现来引用 Collection 对象。也就是说，

ArrayList<Integer> eRemove = new ArrayList<Integer>();

应该是

List<Integer> eRemove = new ArrayList<Integer>();

这样，如果您决定更改为 LinkedList，则只需将代码更改为:

List<Integer> eRemove = new LinkedList<Integer();