Foreach vs Iterator [closed]

Question

I have implemented a trim method which removes objects having empty properties.

This list has average size of 3 or so. Probably, the max length is 7 or 8.

I wonder which of these implementations is faster:

Implementation 1

    private void trim() {
       Iterator<Child> iterator = mList.iterator();
       while (iterator.hasNext()) {
           Child child = iterator.next();
           if (child.isEmpty()) {
               iterator.remove();
           }
       }
   }

Implementation 2

    private void trim() {
       for (Child child : mList) {
           if (child.isEmpty()) {
               mList.remove(child);
           }
       }
   }

Implementation 3

   private void trim() {
      for (int i = 0; i < mList.size(); i++) {
        IChild child = mList.get(i);
        if (child.isEmpty()){
            mList.remove(i);
        }
      }
   }

Answer 1

Implementation 2 will in fact throw ConcurrentModificationException. What comes to Implementation 3, consider you have a list \$1,2,3,4\$, and the third implementation is about to remove \$2\$ and \$3\$. First, the index is 1 and \$2\$ is removed. Now \$3,4\$ is shifted one position to the left so that the entire list is \$1,3,4\$. At this point, the index is 1 and is incremented to 2. Clearly, \$3\$ is omitted and is not removed.

Basically, if removal is done in iteration, your only choice is to use Iterator explicitly.

Hope that helps.