双列集合Map的特点

  1 import java.util.HashMap;
  2 import java.util.Map;
  3 /**
  4  * 双列集合Map的特点:
  5  * 如果键是自定义对象,必须重写equals和hashcode方法  
  6  * @author 罗摩衔那
  7  *
  8  */
  9 public class Demo_Maps
 10 {
 11   public static void main(String[] args) 
 12   {     
 13     //自定义一个容器
 14       Map<IdCard,people>map=new HashMap<>();
 15       //初始两个键
 16       IdCard idcard1=new IdCard("张三丰", "001");
 17       IdCard idcard2=new IdCard("张三丰", "001");
 18       //对应键值
 19       map.put(idcard1, new people("张三丰", "男", "200"));
 20       map.put(idcard2, new people("张三丰", "男", "100"));
 21       System.out.println(map);
 22   }
 23 }
 24 
 25 class people
 26 {
 27     private String name;
 28     private String gender;
 29     private String age;
 30     
 31     public people(String name,String gender,String age)
 32     {
 33         this.name=name;
 34         this.gender=gender;
 35         this.age=age;
 36     }
 37 
 38     @Override
 39     public String toString() {
 40         return "name=" + name + ", gender=" + gender + ", age=" + age ;
 41     }
 42 
 43     @Override
 44     public int hashCode() {
 45         final int prime = 31;
 46         int result = 1;
 47         result = prime * result + ((age == null) ? 0 : age.hashCode());
 48         result = prime * result + ((gender == null) ? 0 : gender.hashCode());
 49         result = prime * result + ((name == null) ? 0 : name.hashCode());
 50         return result;
 51     }
 52 
 53     @Override
 54     public boolean equals(Object obj) {
 55         if (this == obj)
 56             return true;
 57         if (obj == null)
 58             return false;
 59         if (getClass() != obj.getClass())
 60             return false;
 61         people other = (people) obj;
 62         if (age == null) {
 63             if (other.age != null)
 64                 return false;
 65         } else if (!age.equals(other.age))
 66             return false;
 67         if (gender == null) {
 68             if (other.gender != null)
 69                 return false;
 70         } else if (!gender.equals(other.gender))
 71             return false;
 72         if (name == null) {
 73             if (other.name != null)
 74                 return false;
 75         } else if (!name.equals(other.name))
 76             return false;
 77         return true;
 78     }    
 79     
 80 }
 81 
 82 class IdCard
 83 {
 84     private String name;
 85     private String ID;
 86     public  IdCard(String name,String ID)
 87     {
 88         this.name=name;
 89         this.ID=ID;        
 90     }
 91     @Override
 92     public String toString() {
 93         return "name=" + name + ", ID=" + ID ;
 94     }
 95     @Override
 96     public int hashCode() {
 97         final int prime = 31;
 98         int result = 1;
 99         result = prime * result + ((ID == null) ? 0 : ID.hashCode());
100         result = prime * result + ((name == null) ? 0 : name.hashCode());
101         return result;
102     }
103     @Override
104     public boolean equals(Object obj) {
105         if (this == obj)
106             return true;
107         if (obj == null)
108             return false;
109         if (getClass() != obj.getClass())
110             return false;
111         IdCard other = (IdCard) obj;
112         if (ID == null) {
113             if (other.ID != null)
114                 return false;
115         } else if (!ID.equals(other.ID))
116             return false;
117         if (name == null) {
118             if (other.name != null)
119                 return false;
120         } else if (!name.equals(other.name))
121             return false;
122         return true;
123     }
124 }

 1 import java.util.HashMap;
 2 import java.util.Map;
 3 /**
 4  * 双列集合Map的特点:
 5  *  键值对只能是意义对应
 6  *     添加键值对的时候出现了键重复,新的值会把对应的之前的值覆盖
 7  *   
 8  * @author 罗摩衔那
 9  *
10  */
11 public class Demo_Maps
12 {
13   public static void main(String[] args) 
14   {
15      Map<String,String>map=new HashMap<>();
16      map.put("001", "刘亦菲");
17      map.put("002", "迪丽热巴");
18      System.out.println(map);
19      map.put("001", "赵灵儿");
20      System.out.println(map);
21   }
22 }

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原文地址：https://www.cnblogs.com/zjm1999/p/10043119.html