单例模式

1.确保一个类最多有一个实例

2.代码

C++

 1 //Singleton c++
 2 //VS2013 编译通过,MinGW 更新至9.2.0-1 仍报错,
 3 //网站在线编译 https://zh.cppreference.com/w/cpp/thread/mutex
 4 #include 
 5 #include 
 6 #include 

 Java

 1 //Singleton java
 2 class Singleton{
 3     private volatile static Singleton uniqueInstance;
 4     private Singleton(){}
 5     public static Singleton getInstance(){
 6         if(null == uniqueInstance){
 7             synchronized(Singleton.class){                    //synchronized 
 8                 if(null == uniqueInstance)
 9                     uniqueInstance = new Singleton();
10                     count++;
11             }
12         }
13         return uniqueInstance;
14     }
15     public static int count = 0;                            //need static
16 }
17 
18 public class SingleClient{
19     public static void main(String[] args){
20         Singleton single_1 = Singleton.getInstance();
21         Singleton single_2 = Singleton.getInstance();
22         System.out.println("1:" + single_1 + " count:" + single_1.count);
23         System.out.println("2:" + single_2 + " count:" + single_2.count);
24     }
25 }