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javalistconcurrentmodification

Getting a ConcurrentModificationException thrown when removing an element from a java.util.List during list iteration?

@Test
public void testListCur(){
    List<String> li=new ArrayList<String>();
    for(int i=0;i<10;i++){
        li.add("str"+i);
    }

    for(String st:li){
        if(st.equalsIgnoreCase("str3"))
            li.remove("str3");
    }
    System.out.println(li);
}

When I run this code,I will throw a ConcurrentModificationException.

It looks as though when I remove the specified element from the list, the list does not know its size have been changed.

I'm wondering if this is a common problem with collections and removing elements?

Solution

  • I believe this is the purpose behind the Iterator.remove() method, to be able to remove an element from the collection while iterating.

    For example:

    Iterator<String> iter = li.iterator();
while(iter.hasNext()){
    if(iter.next().equalsIgnoreCase("str3"))
        iter.remove();
}