JAVA - 从迭代列表中删除非迭代器元素

Question

我在遍历这个迭代器循环时遇到了一个问题，在这个循环中我遍历了 this.env 的每个元素，但是在这个列表中，想要删除所述列表的不同元素。当我尝试删除所述迭代列表的任何项目时，我收到此错误：java.util.ConcurrentModificationException，据我了解，这是由于修改迭代列表而不使用 iterator.remove ()。

代码：

public void envActions(IOHandler ioHandler, PlayerClass player){
    Iterator<WorldElement> worldElementIterator = this.env.iterator();
    while(worldElementIterator.hasNext()){
        WorldElement worldElement = worldElementIterator.next();
    //for(WorldElement worldElement:this.env){
        if(worldElement instanceof EntityClass){
            EntityClass entity=(EntityClass) worldElement;
            if(entity.nature.contains("hostile")){
                MonsterClass mEntity=(MonsterClass) entity;
                if(!(mEntity.attacks.size()*(Math.random()+0.25)>=mEntity.attacks.size())){
                    Double followerNum = (Math.random()*player.followers.size());
                    Integer followerNumInt=followerNum.intValue();
                    if(followerNumInt<2){
                        PlayerClass target=player;
                        Double attacknumD=mEntity.attacks.size()*Math.random();
                        Integer attacknum= attacknumD.intValue();
                        Integer playerarmor=player.getArmorValue();
                        int enemydamage=mEntity.attacks.get(attacknum).getDamage()*(1-(playerarmor/1000));
                        target.health=target.health-enemydamage;
                        ioHandler.printToConsole("\nThe "+mEntity.name+" attacked you with "+mEntity.attacks.get(attacknum).getAttack()+" and did "+mEntity.attacks.get(attacknum).getDamage()+" damage! you have "+player.health+" health left!");
                    } else {
                        FriendlyCreatureClass target=player.followers.get(followerNumInt);
                        Double attacknumD=mEntity.attacks.size()*Math.random();
                        Integer attacknum= attacknumD.intValue();
                        int enemydamage=mEntity.attacks.get(attacknum).getDamage();
                        target.health=target.health-enemydamage;
                        if(!target.isAlive()){
                            ioHandler.printToConsole("\nThe " + mEntity.name + " attacked " + target.name + " with " + mEntity.attacks.get(attacknum).getAttack() + " and did " + mEntity.attacks.get(attacknum).getDamage() + " damage! " + target.name+" died! Farewell "+target.name+".");
                            target.died(ioHandler, this, player, true);
                            //>>>> THIS IS WHERE I WOUlD LIKE TO REMOVE 'target' FROM THE env LIST <<<<
                        } else {
                            ioHandler.printToConsole("\nThe "+mEntity.name+" attacked "+target.name+" with "+mEntity.attacks.get(attacknum).getAttack()+" and did "+mEntity.attacks.get(attacknum).getDamage()+" damage! "+target.name+" has "+target.health+" health left!");
                        }
                    }
                }

请原谅我的编码技巧，因为我只是 java / Android 的初学者，但非常感谢任何建议！

提前致谢！

Answer 1

我认为它现在可以添加一个 toDelete 列表，检查迭代项是否已经在列表中，如果是，则跳过它，然后将其删除。

我还没有彻底检查错误，但现在没问题。 工作代码：

public void envActions(IOHandler ioHandler, PlayerClass player){
    List<WorldElement> toDelete=new ArrayList<>();
    Iterator<WorldElement> worldElementIterator = this.env.iterator();
    while(worldElementIterator.hasNext()){
        WorldElement worldElement = worldElementIterator.next();
    //for(WorldElement worldElement:this.env){
        if(worldElement instanceof EntityClass && !toDelete.contains(worldElement)){
            EntityClass entity=(EntityClass) worldElement;
            if(entity.nature.contains("hostile")){
                MonsterClass mEntity=(MonsterClass) entity;
                if(!(mEntity.attacks.size()*(Math.random()+0.25)>=mEntity.attacks.size())){
                    Double followerNum = (Math.random()*player.followers.size());
                    Integer followerNumInt=followerNum.intValue();
                    if(followerNumInt<2){
                        PlayerClass target=player;
                        Double attacknumD=mEntity.attacks.size()*Math.random();
                        Integer attacknum= attacknumD.intValue();
                        Integer playerarmor=player.getArmorValue();
                        int enemydamage=mEntity.attacks.get(attacknum).getDamage()*(1-(playerarmor/1000));
                        target.health=target.health-enemydamage;
                        ioHandler.printToConsole("\nThe "+mEntity.name+" attacked you with "+mEntity.attacks.get(attacknum).getAttack()+" and did "+mEntity.attacks.get(attacknum).getDamage()+" damage! you have "+player.health+" health left!");
                    } else {
                        FriendlyCreatureClass target=player.followers.get(followerNumInt);
                        Double attacknumD=mEntity.attacks.size()*Math.random();
                        Integer attacknum= attacknumD.intValue();
                        int enemydamage=mEntity.attacks.get(attacknum).getDamage();
                        target.health=target.health-enemydamage;
                        if(!target.isAlive()){
                            ioHandler.printToConsole("\nThe " + mEntity.name + " attacked " + target.name + " with " + mEntity.attacks.get(attacknum).getAttack() + " and did " + mEntity.attacks.get(attacknum).getDamage() + " damage! " + target.name + " died! Farewell " + target.name + ".");
                            target.died(ioHandler, this, player, false);
                            toDelete.add(target);
                        } else {
                            ioHandler.printToConsole("\nThe "+mEntity.name+" attacked "+target.name+" with "+mEntity.attacks.get(attacknum).getAttack()+" and did "+mEntity.attacks.get(attacknum).getDamage()+" damage! "+target.name+" has "+target.health+" health left!");
                        }
                    }
                }
    for(WorldElement worldElement:toDelete){
        this.env.remove(worldElement);
    }
    return;

感谢您的快速回复！

Answer 2

如果您出于某种原因不使用迭代器，则可以在迭代集合时收集要在集合中删除的元素，并在循环之后迭代集合并从原始集合中删除元素。

请注意，这仅适用于小型集合。

HashSet toDelete = new HashSet();

for (...) {
    if (...)
       toDelete.add(item);
}
// end for

foreach (item in toDelete) {
    // delete from original collection
}

否则，您可以在迭代器上调用 remove()。