在Java中迭代问题时删除

Question

I want to implement a method attack that works like this: every warrior from my troop attacks an warrior chosen randomly from another troop. If the attacked warrior dies it must be removed from the troop. With the method that i tried i get the error for the random number:

 java.lang.IllegalArgumentException: n must be positive

The troop is a List <Creature> warriors; I think that i am not doing the remove correctly, because otherwise i should not have that error.

public void atac(Troop opponentTroop){
        for(Creature f : warriors){
            Creature c = getOpponent(opponentTroop);
            f.atac(c);
            ListIterator<Creature> iterator = opponentTroop.warriors.listIterator();
            while(iterator.hasNext()){
                c = iterator.next();
                if(c.isDead()){
                    iterator.remove();                  
                }
            }   

        }       
    }


private Creature getOpponent(Troop opponent){
        int x = rand.getRandomArrayIndex(opponent.warriors.size());
        return opponent.warriors.get(x);
}

Answer 1

Removing the entry invalidates the iterator. You need to save it, you could do something like this:

while(iterator.hasNext()) {
    c = iterator.next();
    if(c.isDead()) {
        // Make a temporary iterator
        ListIterator<Creature> toDelete= c;
        // Step the regular one
        c = iterator.next();
        // Remove
        toDelete.remove();                  
    }
}   

Also, make sure int x = rand.getRandomArrayIndex(opponent.warriors.size()); never goes beyond the last index (which is the number of entries minus one .