HashMap的三种遍历方式

import java.util.Collection;import java.util.HashMap;import java.util.Iterator;import java.util.Map.Entry;import java.util.Set;public class HashMapDemo {    public static void main(String[] args) {        HashMap map = new HashMap();        //HashMap<Object,Object> map = new HashMap<Object,Object>();        HashMap<Object, Object> map2 = new HashMap<Object, Object>();        //添加--map.put(key,value)        map.put("1001", "张三");        map.put("1002", "李四");        map.put("1003", "Jack");        map.put("1004", "Tom");        //删除--map.remove(key)        Object obj = map.remove("1003");        System.out.println("删除的元素:"+obj);        //修改--put(key,value) ,当key存在        map.put("1002", "赵敏"); //如果key存在则是修改，否则是添加        //查询        //查单个 ---map.get(key)        Object v = map.get("1002"); //如果key所对应位置的value不存在，则返回null        System.out.println("1002:"+v);        //遍历方法1---视图1---map.entrySet()        System.out.println("------视图1---entrySet------------");        Set entries = map.entrySet();        Iterator it = entries.iterator();        while(it.hasNext()){            Entry en = (Entry) it.next();            Object key = en.getKey();            Object value = en.getValue();            System.out.println(key+","+value);        }        //遍历方法2---视图2---map.keySet()        System.out.println("------视图2---keySet------------");        Set set = map.keySet();        Iterator it2 = set.iterator();        while(it2.hasNext()){            Object kk = it2.next();            Object vv = map.get(kk);            System.out.println(kk+","+vv);        }        //如果想避开迭代器来遍历集合(Collection=List或Set),可以转换成数组来进行        System.out.println("------");        Object objs[] = set.toArray();        for(int i=0;i<objs.length;i++){            System.out.println(objs[i]+","+map.get(objs[i]));        }        //遍历方法3---视图3---map.values()--Collection         //values视图只能拿到value,不方便拿到key,我们一般很少使用，抛弃了key优点。        System.out.println("------视图3---values------------");        Collection col = map.values();        Iterator it3 = col.iterator();        while(it3.hasNext()){            Object val = it3.next();            System.out.println(val);        }    }}