Singleton design pattern: (solve that a class only has one object in memory)

Singleton design pattern: (solve that a class only has one object in memory)

Question: How to make a class have only one object in memory?

Thought:

　　1. It is forbidden for other programs to create such objects;
　　2. Since such objects cannot be created externally, they are created in this class;
　　3. In order for other programs to access the objects created in this class, an access method should be provided to the outside world

 

How to use code to reflect (java): (can also be implemented in C++, other languages, etc.)
　　1. Private constructor;
　　2. Create an object in this class;
　　3. Provide a way to access objects of this class to the outside world

Code:

class Object{
    String name;    
    static Object o= new Object();　　//2. Create an object in this class;
     public  static Object getObject(){　　　　//3. Provide the outside world with a method to access the object of this class
         return o;
    }
    private Object(){};　　//1. Private constructor;
}

public class oneObject{
    public static void main(String [] arge){
        Object a = Object.getObject();　　//The first object 
        a.name = "Joke" ;　　　　　　　　　　 //Modify the attribute name in the first object, and also modify the name attribute 
        Object b in the second object = Object.getObject();　　//Second object
        System.out.println(b.name);
    }
}

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