遍历Map的方式

Set keySet()：返回所有key构成的Set集合
Collection values()：返回所有value构成的Collection集合
Set entrySet()：返回所有key-value对构成的Set集合

Map map = new HashMap();
map.put("AA",123);
map.put(45,1234);
map.put("BB",56);

    //遍历所有的key集：keySet()
    Set set = map.keySet();
        Iterator iterator = set.iterator();
        while(iterator.hasNext()){
            System.out.println(iterator.next());
    }
    System.out.println();
    //遍历所有的value集：values()
    Collection values = map.values();
    for(Object obj : values){
        System.out.println(obj);
    }
    System.out.println();
    //遍历所有的key-value
    //方式一：entrySet()
    Set entrySet = map.entrySet();
    Iterator iterator1 = entrySet.iterator();
    while (iterator1.hasNext()){
        Object obj = iterator1.next();
        //entrySet集合中的元素都是entry
        Map.Entry entry = (Map.Entry) obj;
        System.out.println(entry.getKey() + "---->" + entry.getValue());

    }
    System.out.println();
    //方式二：
    Set keySet = map.keySet();
    Iterator iterator2 = keySet.iterator();
    while(iterator2.hasNext()){
        Object key = iterator2.next();
        Object value = map.get(key);
        System.out.println(key + "=====" + value);

    }