Iterating two ArrayLists like in a 2-dimensional Array

Question

I am trying to Iterate two ArrayList: One of them, called "gegner" is a list about enemys and another one called "waende" is about walls.

Whenever a wall and an Enemy touch, both should loose one durability / health. As it didn't work at the same time, I created a new method that should remove the death Objects from the Lists.

My idea was:

public void removeDeathObjects() {
    Wand tempW;
    Gegner tempG;
    for (Iterator<Gegner> it = gegner.iterator(); it.hasNext();) {
        tempG = it.next();
        for (Iterator<Wand> it2 = waende.iterator(); it2.hasNext();) {
            tempW = it2.next();

                if(tempW.isDestroyed()){
                    it2.remove();
                }
                if (tempG.isDeath()){
                    it.remove();
                }
        }   

    }
}

But the program throws an "Exception in thread "AWT-EventQueue-0" in the Line it.remove() java.lang.IllegalStateException" as soon as there are at least two walls, and the enimies aren't killed completely.

Where did I failed?

If you wanted, I could give you the whole code but it's pretty long ._.

PS: sorry for bad English

I don't get why your two loops are nested. Don't you just want something like gegner.removeIf(g -> g.isDeath())? — Julien Lopez
– Julien Lopez, Commented Apr 15, 2016 at 13:02

Julien Lopez · Accepted Answer · 2016-04-15 13:10:53Z

2

Your answer is here: http://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html#remove--

IllegalStateException - if the next method has not yet been called, or the remove method has already been called after the last call to the next method

Instead of iterating manually, you can do this in Java 8:

public void removeDeathObjects() {
    gegner.removeIf(g -> g.isDeath());
    waende.removeIf(w -> w.isDestroyed());
}

answered Apr 15, 2016 at 13:10

Julien Lopez

1,8645 gold badges21 silver badges26 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

vagelis · Accepted Answer · 2016-04-15 13:24:05Z

1

Your mistake is that you have nested two completely independent loops. Looking at your code, it is evident that the inner loop on waende has nothing to do with the outer loop on gegner: your actions on waende do not depend on any check on gegner. What happens is that when tempG.isDeath() is true, it.remove() executes repeatedly, for every Wand in waende. The first removal on the iterator succeeds, but the second fails.

What you need to do is to separate the two loops:

public void removeDeathObjects() {
    Wand tempW;
    Gegner tempG;
    for (Iterator<Gegner> it = gegner.iterator(); it.hasNext();) {
        tempG = it.next();
        if (tempG.isDeath()){
            it.remove();
        }
    }
    for (Iterator<Wand> it2 = waende.iterator(); it2.hasNext();) {
        tempW = it2.next();
        if(tempW.isDestroyed()){
            it2.remove();
        }
    }   
}

edited Apr 15, 2016 at 13:24

answered Apr 15, 2016 at 13:10

vagelis

3343 silver badges9 bronze badges

2 Comments

Julien Lopez Over a year ago

You've swapped the two if blocks. ;-) Fix this and you have my up-vote. And might as well put tempG = it.next() and tempW = it2.next() directly in the for loop.

vagelis Over a year ago

@JulienLopez Bah! Thanks for pointing out my mistake! As for the changes to the for loops, I like to touch questions' code as little as possible, if only to make clearer what I want to say.

Collectives™ on Stack Overflow

Iterating two ArrayLists like in a 2-dimensional Array

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related