HashSet 

 1 package ListSetMapTest;
 2 
 3 import java.util.HashSet;
 4 import java.util.Set;
 5 
 6 public class HashSetTest {
 7     
 8     public static void main(String[] args){
 9         Set<Student> s=new HashSet();
10         s.add(new Student(1,"Tom",15));
11         s.add(new Student(1,"Tom",15));
12         s.add(new Student(1,"Animy",12));
13         s.add(new Student(1,"Tom",11));
14         s.add(new Student(2,"Tom",15));
15         s.add(new Student(3,"Jack",13));
16         
17         for(Student st:s){
18             System.out.println(st+"------->"+st.hashCode());
19         }
20         
21     }
22 
23 }
24 
25 class Student{
26     int no;
27     String name;
28     int age;
29     
30     public Student(int no, String name, int age) {
31         this.no = no;
32         this.name = name;
33         this.age = age;
34     }
35 
36     @Override
37     public String toString() {
38         return "学号： " + no + "姓名：  " + name + "年龄：  " + age ;
39     }
40     
41     
42     
43     
44 }

　　Set集合中不能保存相同的内容，这里值相同但是没有覆盖的原因是两者的哈希值不同，这与HashSet的设计理念不服，因为HashSet是HashMap的key部分，key部分必须唯一。key和value是一一对应的。

       只重写equals()方法：

 1 package ListSetMapTest;
 2 
 3 import java.util.HashSet;
 4 import java.util.Set;
 5 
 6 public class HashSetTest {
 7     
 8     public static void main(String[] args){
 9         Set<Student> s=new HashSet();
10         s.add(new Student(1,"Tom",15));
11         s.add(new Student(1,"Tom",15));
12         s.add(new Student(1,"Animy",12));
13         s.add(new Student(1,"Tom",11));
14         s.add(new Student(2,"Tom",15));
15         s.add(new Student(3,"Jack",13));
16         
17         for(Student st:s){
18             System.out.println(st+"------->"+st.hashCode());
19         }
20         
21     }
22 
23 }
24 
25 class Student{
26     int no;
27     String name;
28     int age;
29     
30     public Student(){
31         
32     }
33     public Student(int no, String name, int age) {
34         this.no = no;
35         this.name = name;
36         this.age = age;
37     }
38 
39     @Override
40     public String toString() {
41         return "学号： " + no + "姓名：  " + name + "年龄：  " + age ;
42     }
43 
44     //重写equals()方法
45     @Override
46     public boolean equals(Object obj) {
47         if(!(obj instanceof Student)){
48          return false;
49         }
50         Student s = (Student)obj;
51         if(this==s){
52             return true;
53         }
54         if(this.name .equals(s.name)&&this.no==s.no&&this.age==s.age){
55             return true;
56         }else
57             return false;
58     }
59 
60     
61     
62     
63     
64 }

 

 

　　equals()和hashCode()方法都重写

 1 package ListSetMapTest;
 2 
 3 import java.util.HashSet;
 4 import java.util.Set;
 5 
 6 public class HashSetTest {
 7     
 8     public static void main(String[] args){
 9         Set<Student> s=new HashSet();
10         s.add(new Student(1,"Tom",15));
11         s.add(new Student(1,"Tom",15));
12         s.add(new Student(1,"Animy",12));
13         s.add(new Student(1,"Tom",11));
14         s.add(new Student(2,"Tom",15));
15         s.add(new Student(3,"Jack",13));
16         
17         for(Student st:s){
18             System.out.println(st+"------->"+st.hashCode());
19         }
20         
21     }
22 
23 }
24 
25 class Student{
26     int no;
27     String name;
28     int age;
29     
30     public Student(){
31         
32     }
33     public Student(int no, String name, int age) {
34         this.no = no;
35         this.name = name;
36         this.age = age;
37     }
38 
39     @Override
40     public String toString() {
41         return "学号： " + no + "姓名：  " + name + "年龄：  " + age ;
42     }
43 
44     
45     @Override
46     public int hashCode() {
47         final int prime = 31;
48         int result = 1;
49         result = prime * result + age;
50         result = prime * result + ((name == null) ? 0 : name.hashCode());
51         result = prime * result + no;
52         return result;
53     }
54     
55 
56     @Override
57     public boolean equals(Object obj) {
58         if(!(obj instanceof Student)){
59          return false;
60         }
61         Student s = (Student)obj;
62         if(this==s){
63             return true;
64         }
65         if(this.name .equals(s.name)&&this.no==s.no&&this.age==s.age){
66             return true;
67         }else
68             return false;
69     }
70 
71     
72     
73     
74     
75 }

相同的值被覆盖

posted @ 2021-01-22 19:38  L1998  阅读(76)  评论(0)    收藏  举报