ArrayList去掉重复值问题

import java.util.ArrayList;import java.util.Hashtable;import java.util.Iterator;public class TestList {public static void main(String[] args){ ArrayList list = new ArrayList(); list.add("1"); list.add("2"); list.add("2"); Iterator it1 = list.iterator(); Hashtable ht = new Hashtable();while(it1.hasNext()){   Object obj = it1.next(); ht.put(obj, obj);  }   Iterator it2 = ht.keySet().iterator(); list = new ArrayList();     while(it2.hasNext()){      list.add(it2.next());  }System.out.println(list.size()); }}