设计模式之单例模式

单例模式的一种实现

将类的所有构造方法都设为private让其无法从外部实例化，然后再内部来实例化一个类，提供一个get方法获取。

 1 public class Student {
 2     private String name;
 3     private String id;
 4 
 5     public String getName() {
 6         return name;
 7     }
 8 
 9     public void setName(String name) {
10         this.name = name;
11     }
12 
13     public String getId() {
14         return id;
15     }
16 
17     public void setId(String id) {
18         this.id = id;
19     }
20 
21     private Student(String name, String id) {
22         this.name = name;
23         this.id = id;
24     }
25 
26     private Student() {
27     }
28 
29     @Override
30     public String toString() {
31         return "Student [name=" + name + ", id=" + id + "]";
32     }
33 
34     private static Student instance = null;
35 
36     public static Student getInstance() {//判断是否存在实例
37         if (instance == null)
38             instance = new Student();
39         return instance;
40     }
41 }

测试：

1 Student student1 = Student.getInstance();//先获取一个学生对象
2 student1.setId("9527");
3 student1.setName("华安");
4 Student student2 = Student.getInstance();//再获取学一个学生对象
5 System.out.println(student1==student2);
6 System.out.println(student2);