Design Patterns (5)--Singleton Pattern

 

Singleton pattern : ensures that a class has only one instance and provides a global access point

 

Singleton has two methods: 1 lazy loading, 2 non-lazy loading

 

package com.em.singleton;

/**
 * Created by Administrator on 2017/12/23.
 */
public class Singleton {

    /*
    * must be a private constructor
    * */
    private  Singleton(){}


    /**
     *
     * non-lazy loading
     * **/
    private static Singleton singleton1 = new Singleton();


    public static Singleton getInstance1(){
        return singleton1;
    }

    /**
     * lazy loading
     *
     * **/
    private static volatile Singleton singleton; //volatile guarantees memory visibility in the case of multiple threads

    public static Singleton getInstance(){
        if(singleton ==null){
            synchronized (Singleton.class){ //Double lock to prevent simultaneous access by multiple threads
                if(singleton==null){
                    singleton = new Singleton();
                    return singleton;
                }
            }
        }
        return singleton;
    }
}