java - 不知道为什么会出现并发修改异常

Question

我正在迭代两个 Orb 对象列表

目前，当我浏览这两个列表时，我会在迭代它们时添加和删除 Orb 对象。

//first I iterate through the "friendly" orb list.
for(orbIterator = friendlyOrbs.listIterator(); orbIterator.hasNext();) {
//I have only included what I (think) is the relevant code.        

Orb tempOrb = orbIterator.next(); //Set a reference to the current orb object so I can update it and use its properties.

        //Some drawing stuff I don't include.

        //The orb is not dead
        int orbResult = tempOrb.Update(); //Updates the orb object and returns its current state.

        if(orbResult == 0) {

        } else if(orbResult == 2) {
            //Died a natural death
            //Stuff to do when the orb dies naturally.
            orbIterator.remove();
        } else if(orbResult == 3) {
            //Killed by player.
            //stuff to do when player kills orb.
            orbIterator.remove();
            orbIterator.add(new Orb(...));
        }
    }

现在这就是我迭代“敌人”球体列表的方式:

   for(orbIterator = enemyOrbs.listIterator(); orbIterator.hasNext();) {
        Orb tempOrb = orbIterator.next();

        int orbResult = tempOrb.Update();

        if(orbResult == 0) {

        } else if (orbResult == 2) {
            //Enemy orb died a natural death.
            orbIterator.remove();

            enemyOrbs.add(...);
        } else if(orbResult == 3) {
            //Enemy orb killed by player.
            orbIterator.remove();
        } else {
            //Draw the orb.
        }
    }

我还有两个计时器任务(一个用于生成友好的球体，一个用于生成敌人的球体)，它们设置一个 boolean 标志，告诉 onDraw 方法是否应该向屏幕添加一个新的球体。

//the friendly orb timertask

public static class FriendlyOrbTimerTask extends TimerTask implements Cloneable {

    @Override
    public void run() {
        if(SystemClock.uptimeMillis() - drawCallTime < 100) {
            Log.i("ADDING NEW ORB", "ADDING NEW ORB");
            friendlyOrbToBeAdded = true;
            friendlyOrbSpawnInterval += 250;
            TIMER.schedule(this.clone(), friendlyOrbSpawnInterval);
        } else {
            pauseStartTime = SystemClock.uptimeMillis();
        }

    }

    @Override
    public FriendlyOrbTimerTask clone(){
        return new FriendlyOrbTimerTask(); //add parameters from the current contextif needed.
    }
}

这是敌人Orb计时器任务:

public static class EnemyOrbTimerTask extends TimerTask implements Cloneable {



    @Override
    public void run() {

        if(SystemClock.uptimeMillis() - drawCallTime < 50) {
            enemyOrbToBeAdded = true;
            enemyOrbSpawnInterval+= 250;
            TIMER.schedule(this.clone(), enemyOrbSpawnInterval);
        }
    }

    @Override
    public EnemyOrbTimerTask clone(){
        return new EnemyOrbTimerTask(); //add parameters from the current contextif needed.
    }
}

以下 if 语句告诉我是否应该向屏幕添加一个新的球体(位于 onDraw 中)

   //These are located right before I iterate through the lists.
   if(friendlyOrbToBeAdded) {
        friendlyOrbs.add(...);
        friendlyOrbToBeAdded = false;
    }
    if(enemyOrbToBeAdded) {
        enemyOrbs.add(...);
        enemyOrbToBeAdded = false;
    }

问题是有时我的应用程序会随机崩溃:

  Orb tempOrb = orbIterator.next(); //This is in the enemyOrb iterator loop.

它给出了异常:java.util.ConcurrentModificationException

我不知道为什么会发生这种情况，因为我正在使用 listIterator.add() 和 listIterator.remove() 这应该允许我避免这些异常。

Answer 1

如果你的复制粘贴是准确的，那么我认为这就是问题所在:

   for(orbIterator = enemyOrbs.listIterator(); orbIterator.hasNext();) {
        ...
            enemyOrbs.add(...);
        ...
   }

您在迭代集合时调用了add。