Map集合常用API复习

 1 package Maptest01;
 2 
 3 import java.util.Collection;
 4 import java.util.HashMap;
 5 import java.util.Map;
 6 import java.util.Set;
 7 
 8 /**
 9  * FileName: MapDemo01
10  * Author:   lps
11  * Date:     2022/4/14 11:07
12  * Sign:刘品水 Q：1944900433
13  */
14 public class MapDemo01 {
15     public static void main(String[] args) {
16         //添加元素：无序 不重复 无索引
17         //Map<String, Integer> maps = new HashMap<>();//一行经典代码
18         Map<String, Integer> maps = new HashMap<>();//一行经典代码
19         maps.put("刘品水",3);
20         maps.put("枸杞",13);
21         maps.put("Java",1);
22         maps.put("Java",100);
23         maps.put("手机",50);
24         //maps.put(null,null);
25 
26         //2.清空集合
27 //        maps.clear();
28 //        System.out.println(maps);
29 
30         //3.查看是否为空
31         System.out.println(maps.isEmpty());
32 
33         //4.根据键获取值 public V get(Object key)
34         Integer key = maps.get("Java");
35         System.out.println(key);
36         //System.out.println(maps.get("Java"));
37 
38         //5.根据键删除整个元素 （删除键会返回键的值）
39         Integer key1 = maps.remove("手机");
40         System.out.println(key1);
41         System.out.println(maps);
42 
43         //6.判断是否包含某个键 包含返回true 反之
44         System.out.println(maps.containsKey("Java"));
45         boolean mobilephone = maps.containsKey("手机");
46         System.out.println(mobilephone);
47 
48 
49         //7.判断是否包含某个值
50         System.out.println(maps.containsValue(13));
51 
52         //8.获取全部键的集合 public Set<K> keyset()
53         Set<String> strings = maps.keySet();
54         System.out.println(strings);
55 
56         //9.获取所有值的集合Collection<V> values();
57         Collection<Integer> values = maps.values();
58         System.out.println(values);
59 
60         //10.集合的大小
61         int size = maps.size();
62         System.out.println(size);
63 
64         //11.合并其他Map集合
65         HashMap<String, Integer> map1 = new HashMap<>();
66         map1.put("Java1",50);
67         map1.put("Java2",2);
68         HashMap<String, Integer> map2 = new HashMap<>();
69         map2.put("Java2",50);
70         map2.put("Java3",2);
71         map1.putAll(map2);//把集合map2的元素拷贝到map1中
72         System.out.println(map1);
73         System.out.println(map2);
74 
75 
76     }
77 }