Java.util.ConcurrentModificationException will be thrown if HashMap, Vector, ArrayList are modified at the same time when iterating.
Single-threaded example (from the network)
public class Test {
public static void main(String[] args) {
ArrayList<Integer> list = new ArrayList<Integer>();
list.add(2);
Iterator<Integer> iterator = list.iterator();
while(iterator.hasNext()){
Integer integer = iterator.next();
if(integer==2)
list.remove(integer);
}
}
}
主要原因在于这个
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
The above example is modified to OK
Iterator<Integer> iterator = list.iterator();
while(iterator.hasNext()){
Integer integer = iterator.next();
if(integer==2)
iterator.remove();
}
Multithreading
1. Add synchronized
2. Use CopyOnWriteArrayList, ConcurrentHasMap instead