exception - ConcurrentModificationException in java ArrayList -


i have following code running on thread:

arraylist<ball> allballs;  arraylist<ball> toremove = new arraylist<ball>();  (ball ball:allballs) { //exception thrown here     ball.move();      if (shouldremove(ball)) {         toremove.add(ball);     } }                allballs.removeall(toremove);        toremove.removeall(toremove);

sometimes throws 

java.util.concurrentmodificationexception   @ java.util.arraylist$arraylistiterator.next(arraylist.java:576)

but when replace line

for (ball ball:allballs) {

by this

for (int i=0; i<allballs.size();i++) {     ball ball = allballs.get(i);

no exception thrown.

why?

only reason getting exception collection getting modified in loop/iteration (i think move method modifying object reflected in list).

to explain why getting exception in foreach not in :

foreach loop uses iterator internally. , collections fail fast (immediately report failure), result of next() method of iterator throw exception if collection getting modified in loop. normal loop not use iterator , reason not getting exception in loop there other side effects of modifying in loop size getting changed or iteration becoming infinite.


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