remove trap in java collection iterator Iterator

package TestList;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.TreeSet;

public class TestIterator {

/**
     * @param args
    */
Public static void main(String[] args) {
// TODO Auto-generated method stub
List list = new ArrayList();
list.add("aaa");
list.add("bbb");
       list.add("ccc");
       Iterator t = list.iterator();
                                                                                    can "bbb")){ //When using iterator to traverse the list collection, if you want to delete an element in any collection, you must delete it when the second to last element is traversed
                                                                                                                                                                                                                                             }
                                                                                                                                 TreeSet< add("fff");
Iterator t1 = set.iterator();
                                                                                                                                                                                                                                  can The elements in a set must be deleted when the first element from the last is traversed
              set.remove("eee"); The difference, therefore, causes List and Set to behave differently when deleting collection elements while iterating.