Java in , If we create a class , I want this class to have only one object , Then we can

1: The construction method of this class is designed as private

2: Define a static Method , Create objects in this method

package test;
* Sometimes we want a class to have only one instance at any time , At this time, we can design this class as singleton pattern .
* To design a class as a singleton pattern , need :
* 1: The access modifier of the constructor of this class is private
* 2: Then define a static Method , Create the object of the class in this method
* */
public class Singleton {
private static final Singleton INSTANCE = new Singleton(); // Private member
private int a = 0;// Private member private Singleton(){}// Construction method
public static synchronized Singleton getInstance(){// Class method
return INSTANCE;
public void methodA(){ // Member method
System.out.println("a = "+a);
public static void main(String[] args){ // Main method
Singleton sg1 = Singleton.getInstance();
Singleton sg2 = Singleton.getInstance();
System.out.println(sg1 == sg2);
} }

java There can only be one instance of the class creation in

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