单例设计模式

 1 class Single
 2 {
 3     private int age;
 4 
 5     public void setAge(int num)
 6     {
 7         this.age = num;
 8     }
 9 
10     public int getAge()
11     {
12         return age;
13     }
14 
15     Single(){}                    //构造函数若私有化既 private Single(){} 则不能对对象进行初始化(无法创建新对象)
16 
17     private static Single s = new Single ();
18 
19     public static Single getInstance()                //提供访问方式
20     {
21         return s;
22     }
23     /*
24     除非在类中创建更改成员变量的方法  否则无法对成员变量进行任何修改
25     */
26 }
27 
28 class SingleDemo
29 {
30     public static void main(String [] args)
31     {
32         Single s1 = Single.getInstance();
33         Single s2 = Single.getInstance();
34         
35         s1.setAge(20);
36         System.out.println(s2.getAge());                //指向同一对象在堆内存中
37 
38         Single s3 = new Single();
39         Single s4 = new Single();
40 
41         s3.setAge(30);                                    
42         System.out.println(s4.getAge());
43     }
44 }