Java Set gets full

Question

I am making a particle emitter. Every "Rendered" object is stored in a HashSet, and when there's lots of particles on the screen, the console spits out concurrent modification exceptions. I usually have a short lifetime on these particles so they get deleted after several seconds, but I am sure this could potentially be a problem in the future. How can I fix this?

EDIT: Code:

public class UpdatedManager {
private static Set<Updated> updates = new HashSet<>();

private UpdatedManager() {}

public static Set<Updated> getUpdates() {
    return new HashSet<Updated>(updates);
}
public static boolean registerUpdated(Updated u) {
    return updates.add(u);
}
public static boolean unregisterUpdated(Updated u) {
    return updates.remove(u);
}
public static void update() {
    for (Updated up : new HashSet<Updated>(updates))
        up.update();
}
public static Set<GameObject> getGameObjects() {
    Set<GameObject> objs = new HashSet<>();
    for (Updated up : new HashSet<Updated>(updates)) {
        if (up instanceof GameObject)
            objs.add((GameObject) up);
    }
    return objs;
}
public static Set<GameObject> getGameObjectsByName(String name) {
    Set<GameObject> objs = new HashSet<>();
    for (GameObject go : new HashSet<GameObject>(getGameObjects())) {
        if (go.getName() != null && go.getName().equals(name))
            objs.add(go);
    }
    return objs;
}
public static Set<Particle> getParticles() {
    Set<Particle> parts = new HashSet<>();
    for (Updated up : new HashSet<Updated>(updates)) {
        if (up instanceof Particle)
            parts.add((Particle) up);
    }
    return parts;
}
}

ConcurrentModificationException usually happens when you are making changes to a set, like deleting elements, while at the same time iterating over the set. You need to redesign your approach to the problem. — Vincent Ramdhanie, Dec 08 '14 at 22:50

score 1 · Answer 1 · answered Dec 08 '14 at 23:03

1

A ConcurrentModificationException means you modified the set while iterating over it. It does not mean the set is full.

For example, the following code will throw a ConcurrentModificationException:

Set<String> set = new HashSet<>();

set.add("Hello");

for(String s : set)
    set.add(s+" world");

Note that you are not guaranteed to get a ConcurrentModificationException, so you should avoid catching it. You should instead fix your code so that it doesn't cause the problem.

answered Dec 08 '14 at 23:03

user253751

57,427
7
48
90

I loop through a copy of the set, not the actually set. – MCMastery Dec 08 '14 at 23:04
1

@MCMastery If you loop through a copy of the set (as in `for(String s : new HashSet<>(set))` then you don't get a ConcurrentModificationException (because you're not modifying the copy). You get a ConcurrentModificationException, therefore you are not looping through a copy of the set. – user253751 Dec 08 '14 at 23:06
Where it says the error occurs, it is a copy. I'll double check again – MCMastery Dec 08 '14 at 23:08

score -1 · Answer 2 · answered Dec 08 '14 at 22:59

-1

What makes you think that the set is full?

Concurrent modification exceptions mean that the set is being accessed by different threads in an unsafe manner.

Try a synchronised set using the Collections utilities

HashSet hashSet = new HashSet();
Set set = Collections.synchronizedSet(hashSet);

or use the synchronized keyword for the method accessing the set.

answered Dec 08 '14 at 22:59

dovidzeev

27
4

I downvoted this for suggesting that synchronizedSet will solve all the OP's problems, without knowing the root cause. synchronizedSet will not solve all ConcurrentModificationException problems. Even the ones cause by multithreading. – user253751 Dec 08 '14 at 23:07

Java Set gets full

2 Answers2

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