1 import java.util.*;
 2
 3 public class HashMapTest{
 4     public static void main(String[] args){
 5         //HashMap只考虑key的存储,它对key的存储机制,几乎与HashSet的机制相同,add每放一次都仅一个值,put可放key-value对
 6         //如果希望HashMap记住我们添加元素的顺序,应该考虑使用LinkedHashMap
 7         HashMap<String,double> test = new HashMap<>();
 8
 9         //对于Map而言，每次添加都要key-value对
10         test.put("语文",88.0);
11         test.put("数学",99.0);
12         test.put("英语",78.0);
13
14         System.out.println(test.size());
15         System.out.println(test);
16     }
17 }

 1 import java.util.*;
 2
 3 class Person{
 4     private String name;
 5     private double height;
 6     public Person(String name, double height){
 7         this.name = name;
 8         this.height = height;
 9     }
10
11     @Override
12     public String toString(){
13         return "他/她是：" + name + "身高是：" + height;
14     }
15
16     @Override
17     public boolean equals(Object obj){
18         if(this == obj){
19             return true;
20         }
21         //判断关键属性是否相等
22         if(obj != null && obj.getClass() == Person.class){
23             Person p = (Person)obj;
24             return this.height = p.height && this.name.equals(p.name);
25         }
26         return false;
27     }
28
29     @Override
30     public int hashCode(){
31         return name.hashCode() + 10*(int)height;
32     }
33 }
34
35 public class TestHashMap{
36     public static void main(String[] args){
37         HashMap<Person,double> hs = new HashMap<>();
38
39         hs.put(new Person("James",180),77);
40         hs.put(new Person("Polo",171),76);
41         hs.put(new Person("James",180),77);
42
43         System.out.println(hs);
44     }
45 }

 1 public class TreeMapTest{
 2     public static void main(String[] args){
 3         //如果创建TreeMap时没有传入Comparator对象，说明用的是自然排序
 4         //因为String已经实现了Comparable接口
 5         TreeMap<String , Double> test = new TreeMap<>();
 6
 7         //对于Map而言，每次添加都要key-value对
 8         test.put("aaa",88.0);
 9         test.put("abc",99.0);
10         test.put("xyz",78.0);
11
12         System.out.println(test);
13     }
14 }

 1 import java.util.*;
 2
 3 class TestForMap {
 4     public static void main(String[] args){
 5         HashMap<String, String> hp = new HashMap<String, String>();
 6         hp.put("username","hp");
 7         hp.put("password","12345");
 8         hp.put("email","hp@hp.com");
 9         hp.put("UserID","358");
10
11         //keySet()方式使用for循环遍历Map
12         for(String key : hp.keySet()){
13             //循环遍历Map的key值
14             System.out.println(key);
15             //循环遍历Map中key对应的value值
16             //System.out.println(hp.get(key));
17         }
18
19         Iterator<String> it = hp.keySet().iterator();
20         while(it.hasNext()){
21             //循环遍历Map的key值
22             //System.out.println(it.next());
23             //循环遍历Map中key对应的value值
24             System.out.println(hp.get(it.next()));
25         }
26     }
27 }