不知道為什么會有並發修改異常

Question

我正在遍歷兩個Orb對象列表

目前，當我瀏覽兩個列表時，我在遍歷它們時添加和刪除了Orb對象。

//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(...));
        }
    }

現在，這就是我遍歷“敵人”球列表的方式：

   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.
        }
    }

我還有兩個計時器任務（一個用於生成友好的球，一個用於生成敵人的球），它們設置了一個布爾標志，該標志告訴onDraw方法是否應該向屏幕添加新的球。

//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.
    }
}

這是敵人的球計時器任務：

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.
    }
}

這是if語句，告訴我是否應在屏幕上添加新的球體（位於onDraw中）

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

問題是有時我的應用程序隨機崩潰，並顯示以下內容：

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

它給出了異常： java.util.ConcurrentModificationException

我不知道為什么會這樣，因為我正在使用listIterator.add()和listIterator.remove() ，這應該允許我避免這些異常。

Answer 1

如果您的復制粘貼正確，那么我認為這就是問題所在：

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

在迭代集合時，您可以致電add集合。