链表-Java项未从LinkedList中删除

Question

我正在开发一款简单的视频游戏，很快就遇到了一个无法解决的问题。。。我的游戏中有很多敌人，所以它们当然都继承自一个类Enemy。但当玩家和敌人发生碰撞时，敌人不会被移除。。。这是我的Entity、BlueEnemy、Controller和Enemy代码。我假设我的Player类是可以的，因为当它们碰撞时，我的玩家会消失。

Entity.java

package com.darksunproductions.ld47.Entities;
import java.awt.Point;
import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;
import com.darksunproductions.ld47.Game.Game;
public class Entity {
    private int x;
    private int y;
    private Point pos;
    private double velX;
    private double velY;
    private BufferedImage icon;
    private boolean dead = false;
    private int updatesSinceDeath = -1;
    protected Game game;
    protected Entity(int x, int y, double velX, double velY, Game game, BufferedImage icon){
        this.x = x;
        this.y = y;
        this.velX = velX;
        this.velY = velY;
        this.game = game;
        this.icon = icon;
    }
    public void setUpdatesSinceDeath(int i){
        updatesSinceDeath = i;
    }
    public int getUpdatesSinceDeath(){
        return updatesSinceDeath;
    }
    public boolean isDead(){
        return dead;
    }
    public void kill(){
        dead = true;
        updatesSinceDeath = 0;
        try{
            icon = ImageIO.read(new File("Explosion.png"));
        }catch(Exception e){
            e.printStackTrace();
        }
    }
    public Point topLeft(){
        return new Point(x, y);
    }
    public Point topRight(){
        return new Point(x+icon.getWidth(), y);
    }
    public Point bottomLeft(){
        return new Point(x, y+icon.getHeight());
    }
    public Point bottomRight(){
        return new Point(x+icon.getWidth(), y+icon.getHeight());
    }
    public void setX(int x){
        this.x = x;
    }
    public int getX() {
        return x;
    }
    public int getY() {
        return y;
    }
    public void setY(int y){
        this.y = y;
    }
    public double getVelX() {
        return velX;
    }
    public void setVelX(double velX) {
        this.velX = velX;
    }
    public double getVelY() {
        return velY;
    }
    public void setVelY(double velY) {
        this.velY = velY;
    }
    public BufferedImage getIcon() {
        return icon;
    }
    public void setIcon(BufferedImage icon) {
        this.icon = icon;
    }
}

BlueEnemy.java

package com.darksunproductions.ld47.Entities;
import java.io.File;
import javax.imageio.ImageIO;
import com.darksunproductions.ld47.Game.Drawable;
import com.darksunproductions.ld47.Game.Game;
public class BlueEnemy extends Enemy implements Drawable{
    public BlueEnemy(int x, int y, double velX, double velY, Game game){
        super(x, y, velX, velY, game, null, Type.BLUE);
        try{
            setIcon(ImageIO.read(new File("Blue_Enemy.png")));
        }catch(Exception e){
            setIcon(null);
        }
    }
}

Controller.java

package com.darksunproductions.ld47.Game;
import java.awt.Graphics;
import java.awt.Point;
import java.util.LinkedList;
import com.darksunproductions.ld47.Entities.Enemy;
import com.darksunproductions.ld47.Entities.Entity;
import com.darksunproductions.ld47.Entities.Player;
public class Controller {
    LinkedList<Drawable> entities = new LinkedList<Drawable>();
    Game game;
    public Controller(Game g){
        game = g;
    }
    public void testCollision(int startID){
        if(entities.size() > 0){
            Entity e1 = (Entity) entities.get(startID);
            Point corner[] = new Point[4];
            corner[0] = e1.topLeft();
            corner[1] = e1.topRight();
            corner[2] = e1.bottomLeft();
            corner[3] = e1.bottomRight();
            for (int e = startID + 1; e < entities.size(); e++) {
                Entity e2 = (Entity) entities.get(e);
                for (int c = 0; c < 4; c++) {
                    if (corner[c].x > e2.topLeft().x && corner[c].x < e2.topRight().x) {
                        if (corner[c].y > e2.topLeft().y && corner[c].y < e2.bottomLeft().y) {
                            collide(e1, e2);
                        }
                    }
                }
            }
        }
    }
    public void collide(Entity e1, Entity e2){
        if(e1 instanceof Player && !e1.isDead()){
            if(e2 instanceof Enemy && !e2.isDead()){
                e1.kill();
                e2.kill();
            }
        }
    }
    public void update(){
        if(entities.size() > 0){
            for(Drawable d : entities)
                d.update();
        }
    }
    public void render(Graphics g){
        if(entities.size() > 0){
            for(Drawable d : entities)
                d.render(g);
        }
    }
    public void add(Drawable d){
        entities.add(d);
    }
    public void remove(Drawable d){
        entities.remove(d);
    }
    public void remove(int i){
        entities.remove(i);
    }
    public int size(){
        return entities.size();
    }
    public int getIdOf(Entity e){
        for(int i = 0; i < entities.size(); i++){
            if(e == (Entity)entities.get(i))
                return i;
        }
        return -1;
    }
    public int getIdOf(Drawable d){
        Entity e = (Entity)d;
        for(int i = 0; i < entities.size(); i++){
            if(e == (Entity)entities.get(i))
                return i;
        }
        return -1;
    }
}

Enemy.java

package com.darksunproductions.ld47.Entities;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import com.darksunproductions.ld47.Game.Drawable;
import com.darksunproductions.ld47.Game.Game;
public class Enemy extends Entity implements Drawable{
    public enum Type{
        BLUE
    }
    private Type type;
    public Enemy(int x, int y, double velX, double velY, Game game, BufferedImage icon, Type type){
        super(x, y, velX, velY, game, icon);
        this.type = type;
    }
    public void render(Graphics g){
        if(getIcon() != null)
            g.drawImage(getIcon(), getX(), getY(), null);
    }
    public void update(){
        if(getUpdatesSinceDeath() < 0){
            setY(getY() + (int)getVelY());
            if(getY() > 550){
                setY(-50);
                setX((int)(Math.random()*468));
            }
        }else if(getUpdatesSinceDeath() >= 0){
            setUpdatesSinceDeath(getUpdatesSinceDeath() + 1);
            if(getUpdatesSinceDeath() > 60){
                game.c.remove(this);
            }
        }
    }
}

当它们碰撞时，我遇到的问题是：

Exception in thread "Thread-1" java.util.ConcurrentModificationException
    at java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:778)
    at java.util.LinkedList$ListItr.next(LinkedList.java:713)
    at com.darksunproductions.ld47.Game.Controller.update(Controller.java:52)
    at com.darksunproductions.ld47.Game.Game.update(Game.java:58)
    at com.darksunproductions.ld47.Game.Game.run(Game.java:78)
    at java.lang.Thread.run(Thread.java:701)

除了一个小问题。。。当我点击LinkedList.java:778时，Eclipse说LinkedList没有第778行。。。

提前感谢您的帮助。。。

Answer 1

game.c.remove(this);是不良设计的良好指标，实体不负责决定何时删除它，只负责向Controller提供可以使用的信息

主要的问题是，增强的循环涉及List的Iterator，这阻止了在对其进行迭代时对底层List进行修改

相反，您自己使用List的Iterator，当Controller确定某个实体已失效（已失效或曾经失效）时，使用Iterator的remove方法将其删除，例如

public void update(){
    if(entities.size() > 0){
        LinkedList<Drawable> entities = new LinkedList<>();
        while (it.hasNext()) {
            Drawable d = it.next();
            d.update();
            // Or what ever flag you want to use
            if (d.isRemovable()) {
                it.remove(d);
            }
        }
    }
}

Answer 2

我假设game.c是BlueEnemy类中的控制器，在这种情况下，您将在控制器中循环访问可能要删除的列表。这就是并发修改异常的原因。您可以循环浏览列表的副本，这将是一个解决方法。