容器遍历之迭代器的使用

一个简单的main函数demo来记录下：

public static void main(String args[]){
        ArrayList<Integer>list=new ArrayList<>();
        list.add(1);
        list.add(2);
        list.add(3);
        list.add(4);
       for(Iterator<Integer> it=list.iterator();it.hasNext();){
           int tmp=it.next();
           System.out.println(tmp);
       }

        HashMap<String,String>map=new HashMap<>();
        map.put("语文","90");
        map.put("数学","80");
        map.put("英语","100");
        Set<String>keys=map.keySet();
        for(Iterator<String>it=keys.iterator();it.hasNext();){
            String tmp=it.next();
            System.out.println("key is "+tmp);
            System.out.println("value is "+map.get(tmp));
        }
          Set<Map.Entry<String,String>> enter=map.entrySet();
        for(Iterator it=enter.iterator();it.hasNext();){
            System.out.println(it.next());
        }
    }