不确定为什么会出现并发修改异常

Question

我正在遍历两个 Orb 对象列表

目前，当我浏览这两个列表时，我会在遍历它们时添加和删除 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(...));
        }
    }

现在这就是我遍历 "enemy" orb 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），它们设置了一个布尔标志，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 enemyOrb 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.
    }
}

以下是 if 语句，告诉我是否应该向屏幕添加一个新球体（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在以下行随机崩溃：

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

它给出了例外：java.util.ConcurrentModificationException

我不知道为什么会这样，因为我正在使用 listIterator.add() 和 listIterator.remove()，这应该可以让我避免这些异常。

Answer 1

如果你的复制粘贴是准确的，那么我认为是这个问题：

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

您在迭代集合时调用了集合 add。

不确定为什么会出现并发修改异常

Not sure why there is concurrent modification exception

java

android

concurrentmodification