java之hashSet

 1 import java.util.HashSet;
 2 import java.util.Set;
 3 
 4 
 5 public class demo {
 6     public static void main(String[] args) {
 7         Set<Test> set = new HashSet<Test>();
 8         Test test = new Test();
 9 
10         test.setStr("123");
11         set.add(test);
12         System.out.println(set);
13 
14         test.setStr("456");
15         set.add(test);
16         System.out.println(set);
17 
18         test.setStr("789");
19         set.add(test);
20         System.out.println(set);
21     }
22 }
23 class Test{
24     String str;
25 
26     public void setStr(String str) {
27         this.str = str;
28     }
29 
30     @Override
31     public String toString() {
32         return str;
33     }
34 
35     @Override
36     public int hashCode() {
37         return str.hashCode();
38     }
39 
40 }

这段代码将会输出

[123]
[456, 456]
[789, 789, 789]

所以java的集合加入的是引用，大概是为了节约时间吧

如果要插入对象，就应该不断创建对象的引用

 1 import java.util.HashSet;
 2 import java.util.Set;
 3 
 4 
 5 public class demo {
 6     public static void main(String[] args) {
 7         Set<Test> set = new HashSet<Test>();
 8         Test test = new Test();
 9 
10         test.setStr("123");
11         set.add(test);
12         System.out.println(set);
13 
14         test = new Test();
15         test.setStr("456");
16         set.add(test);
17         System.out.println(set);
18 
19         test = new Test();
20         test.setStr("789");
21         set.add(test);
22         System.out.println(set);
23     }
24 }
25 class Test{
26     String str;
27 
28     public void setStr(String str) {
29         this.str = str;
30     }
31 
32     @Override
33     public String toString() {
34         return str;
35     }
36 
37     @Override
38     public int hashCode() {
39         return str.hashCode();
40     }
41 
42 }

[123]
[123, 456]
[123, 456, 789]