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

Question

@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?

Answer 1

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(); } 

Answer 2

The Java 8 way to remove it from the List without Iterator is:

li.removeIf(<predicate>) 

i.e.

List<String> li = new ArrayList<String>(); // ... li.removeIf(st -> !st.equalsIgnoreCase("str3"));