concurrentmodification

I've searched StackOverflow and there are many ConcurrentModificationException questions. After reading them, I'm still confused. I'm getting a lot of these exceptions. I'm using a "Registry" setup to keep track of Objects: public class Registry { public static ArrayList<Messages> messages = new ArrayList<Messages>(); public static ArrayList<Effect> effects = new ArrayList<Effect>(); public static ArrayList<Projectile> proj = new ArrayList<Projectile>(); /** Clears all arrays */ public static void recycle(){ messages.clear(); effects.clear(); proj.clear(); } } I'm adding and removing objects

This question already has an answer here: Why is a ConcurrentModificationException thrown and how to debug it 7 answers I was reading about ConcurrentModificationException and how to avoid it. Found an article . The first listing in that article had code similar to the following, which would apparently cause the exception: List<String> myList = new ArrayList<String>(); myList.add("January"); myList.add("February"); myList.add("March"); Iterator<String> it = myList.iterator(); while(it.hasNext()) { String item = it.next(); if("February".equals(item)) { myList.remove(item); } } for (String item

I have a for loop like for (int neighbour : neighbours) { Where I may modify neighbours within the loop. Found that thats the cause of ConcurrentModificationException . And read from https://stackoverflow.com/a/8189527/292291 Hence if you want to modify the list (or any collection in general), use iterator , because then it is aware of the modifications and hence those will be handled properly. So I tried: neighboursItr = neighbours.iterator(); while (neighboursItr.hasNext()) { // try disconnecting vertices neighbour = neighboursItr.next(); But that doesnt fix the problem. Why? Are you calling

I have a class like the following: class Test { private LinkedList<Person> persons = new LinkedList<Person>; public synchronized void remove(Person person) { persons.remove(person); } public List<Person> getAllPersons() { // Clients may iterate over the copy returned and modify the structure. return new ArrayList<Person>(persons); } } persons may be modified concurrently: one is via remove() by one thread and two via the shallow copied instance returned by getAllPersons() . I have tested the above scenario in a multithreaded environment to see if I can avoid ConcurrentModificationException by

I found this question in a textbook I am reading. The solution is given below it as well. I'm having trouble understanding how the minimum could be 2. Why couldn't a thread read 0, all other threads execute and it writes 1? And whether it is 1 or 2, the thread writing last must still complete its own loop? int n = 0; int main(int argc, char **argv) { for (i = 0; i < 5; i++) { int tmp = n; tmp = tmp + 1; n = tmp; } return 0; } If a single thread ran this application, you would expect the final output to be 5. What if 5 threads ran the same loop in parallel? What are the largest and smallest

ArrayList<Integer> targets = new ArrayList<Integer>(); targets.add(2); targets.add(2); for (Integer testInt : targets ) { targets.add(1); } I am getting an concurrentModificationException,But with normal for loop. I am not getting any exception. in normal forloop like:- for(int i=0;i<target.size();i++) { System.out.println(target.get(i)); target.add(22); //no exception target.remove(2) // no exception } ForEach loop won't loop directly on your collection. It uses the iterator of your collection behind. you can see the iterator in your collections implementation. From Arraylist source code 735