java - Iterating through a Collection, avoiding ConcurrentModificationException when removing in loop -

we know can't this:

for (object : l) {     if (condition(i)) {         l.remove(i);     } } 

concurrentmodificationexception etc... apparently works sometimes, not always. here's specific code:

public static void main(string[] args) {     collection<integer> l = new arraylist<integer>();      (int i=0; < 10; ++i) {         l.add(new integer(4));         l.add(new integer(5));         l.add(new integer(6));     }      (integer : l) {         if (i.intvalue() == 5) {             l.remove(i);         }     }      system.out.println(l); } 

this, of course, results in:

exception in thread "main" java.util.concurrentmodificationexception 

... though multiple threads aren't doing it... anyway.

what's best solution problem? how can remove item collection in loop without throwing exception?

i'm using arbitrary collection here, not arraylist, can't rely on get.

iterator.remove() safe, can use this:

list<string> list = new arraylist<>();  // clever way create iterator , call iterator.hasnext() // in while-loop. same doing: //     iterator<string> iterator = list.iterator(); //     while (iterator.hasnext()) { (iterator<string> iterator = list.iterator(); iterator.hasnext();) {     string string = iterator.next();     if (string.isempty()) {         // remove current element iterator , list.         iterator.remove();     } } 

note iterator.remove safe way modify collection during iteration; behavior unspecified if underlying collection modified in other way while iteration in progress.

source:

http://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html

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and similarly, if have listiterator , want add items, can use listiterator#add, same reason can use iterator#remove — it's designed allow it.