class ArrayListTest1 {     public static void main(String[] args) {         ArrayList al = new ArrayList();         al.add("java03");         al.add("java03");         al.add("java01");         al.add("java02");         al.add("java01");         al.add("java02");         al.add("java01");         System.out.println(al);         al = singleElement(al);         System.out.println(al);     }     //返回List合适些     public static ArrayList singleElement(ArrayList al){       //定义一个临时容器       ArrayList newAl = new ArrayList();       //在迭代是循环中next调用一次，就要hasNext判断一次       Iterator it = al.iterator();        while (it.hasNext()){          Object obj = it.next();//next()最好调用一次就hasNext()判断一次否则容易发生异常          if (!newAl.contains(obj))             newAl.add(obj);         }         return newAl;     } }