Four ways to get a single case

A singleton pattern is often used in the project, which summarizes

1-A Hungry man

 Public class Singleton  {    // a hungry man type    Private Singleton () {            }    privatestaticnew  Singleton ();      Public Static Singleton getinstance () {        return  Singleton;    }    }

2 Lazy Thread-safe

 Public classSingleton {//Lazy Type    PrivateSingleton () {}Private StaticSingleton Singleton =NULL;  Public Static synchronizedSingleton getinstance () {if(singleton==NULL){            return NewSingleton (); }        returnSingleton; }}

3 Two-Lieutenant, thread-safe.

 Public classSingleton {//double check     PrivateSingleton () {}Private Static volatileSingleton Singleton =NULL;  Public StaticSingleton getinstance () {if(singleton==NULL){             synchronized(Singleton.class){                 if(singleton==NULL) {                    return NewSingleton (); }             }         }        returnSingleton; }}

4 static internal classes are nested class thread-safe

 Public class Singleton {        private  Singleton () {}        privatestaticclass  instanceholder{        privatestaticnew  Singleton ();    }     publicstatic  Singleton getinstance () {        return  Instanceholder.singleton;}    }

Synchronized will affect service performance, why it will affect, not too clear, later understand in the supplement. Static inner classes (nested classes) are better in comparison

Four ways to get a single case