Java自学笔记：Map集合

public class Map1 {
    public static void main(String[] args) {
        Map<String,Integer> map1 = new HashMap<String,Integer>();
        map1.put("a",1);
        map1.put("r",4);
        map1.put("q",8);
        map1.put("c",6);
        System.out.println(map1);
        //通过键值来删除键值对
        map1.remove("r");
        System.out.println(map1);
        //map1的长度
        System.out.println(map1.size());
        //判断当前的map集合是否包含指定key
        System.out.println(map1.containsKey("j"));
        //判断当前的map集合是否包含指定value
        System.out.println(map1.containsValue(4));

        Set<String> map=map1.keySet();//获取map集合的key的集合
//        map1.values();//获取集合的所有value

        for (String m: map){
            System.out.println("key:"+ m+"  value:"+map1.get(m));
            System.out.println("====================");

            
        }
    }
}

输出结果： 

{a=1, q=8, r=4, c=6}
{a=1, q=8, c=6}
3
false
false
key:a  value:1
key:q  value:8
key:c  value:6
====================

TreeMap:

public class Test {
    public static void main(String[] args) {
        //TreeMap的自然排序是字典排序
        Map<Integer,String> tree1 = new TreeMap<Integer,String>();
        tree1.put(17, "a");
        tree1.put(12, "ac");
        tree1.put(16, "aw");
        tree1.put(18, "art");
        tree1.put(142, "aj");
        System.out.println(tree1);
    }
}

输出结果：

{12=ac, 16=aw, 17=a, 18=art, 142=aj}