Java single-instance mode implementation

A class that can only generate one instance is a class that implements the singleton (singleton) pattern. Here's how to implement a singleton pattern in C #

Mode one is only used in single-threaded environments

Set the constructor as a private function to prevent others from creating instances//Define a static instance, create the instance when needed//in Singleton static property instance, only create an instance when instance is null to avoid duplicate creation//  Define the constructor as private function public final class Singleton1 {private Singleton1 () {}private static Singleton1 _instance = Null;public static Singleton1 getinstance () {if (_instance = = null) _instance = new Singleton1 (); return _instance;} public static void Main (string[] args) {Singleton1 S1 = singleton1.getinstance (); Singleton1 s2 = singleton1.getinstance (); System.out.println (S1.hashcode ()); System.out.println (S2.hashcode ());}}

Mode two plus synchronous lock

import java.util.concurrent.locks.lock;import  java.util.concurrent.locks.reentrantlock;public final class singleton2 {private  Singleton2 () {}static lock lock = new reentrantlock ();p rivate static  Singleton2 _instance = null;public static singleton2 getinstance () {lock.lock (); Try {if (_instance == null) _instance = new singleton2 ();}  finally {lock.unlock ();} Return _instance;} Public static void main (String[] args)  {Singleton2 s1 =  Singleton2.getinstance (); Singleton2 s2 = singleton2.getinstance (); System.out.println (S1.hashcode ()); System.out.println (S2.hashcode ());}} 

Feasible solution plus synchronous lock two times before and after the instance has been determined whether it exists

import java.util.concurrent.locks.lock;import  java.util.concurrent.locks.reentrantlock;public final class singleton3 {private  Singleton3 () {}static lock lock = new reentrantlock ();p rivate static  Singleton3 _instance = null;public static singleton3 getinstance () {if (_instance  == null) {lock.lock (); Try{if (_instance == null) _instance = new singleton3 () ;} Finally {lock.unlock ();}} Return _instance;} Public static void main (String[] args)  {Singleton3 s1 =  Singleton3.getinstance (); Singleton3 s2 = singleton3.getinstance (); System.out.println (S1.hashcode ()); System.out.println (S2.hashcode ());}} 

The recommended solution is to use a static constructor

Public final class Singleton4 {private Singleton4 () {}private static Singleton4 _instance = new Singleton4 ();p ublic static Singleton4 getinstance () {return _instance;} public static void Main (string[] args) {Singleton4 S1 = singleton4.getinstance (); Singleton4 s2 = singleton4.getinstance (); System.out.println (S1.hashcode ()); System.out.println (S2.hashcode ());}}

Recommended solution Two implementations create instances on demand

public class Singleton5 {private Singleton5 () {}public static Singleton5 getinstance () {return nested.instance;} private static Class Nested{private Nested () {}public static final Singleton5 instance = new Singleton5 ();} public static void Main (string[] args) {Singleton5 S1 = singleton5.getinstance (); Singleton5 s2 = singleton5.getinstance (); System.out.println (S1.hashcode ()); System.out.println (S2.hashcode ());}}

1. Extended

    定义一个表示总统的类型President可以从该类型继承出FrenchPresident和AmericanPresident等类型。这些派生类型都只能产生一个实例        

Public class president {private string _name;public president () {}public  String getname () {return _name;} Public void setname (string name) {_name = name;} Public static void main (String[] args)  {}}public class frenchpresident  extends president{private frenchpresident () {}public static frenchpresident  GetInstance () {return nested.instance;} Private static class nested{private nested () {}public static final  Frenchpresident instance = new frenchpresident ();} Public static void main (String[] args)  {FrenchPresident s1 =  Frenchpresident.getinstance (); Frenchpresident s2 = frenchpresident.getinstance (); System.out.println (S1.hashcode ()); System.out.println (S2.hashcode ());}} Public class americanpresident {private americanpresident ()  {}pUblic static americanpresident getinstance ()  {return nested.instance;} Private static class nested {private nested ()  {}public static final  americanpresident instance = new americanpresident ();} Public static void main (String[] args)  {AmericanPresident s1 =  Americanpresident.getinstance (); Americanpresident s2 = americanpresident.getinstance (); System.out.println (S1.hashcode ()); System.out.println (S2.hashcode ());}}

This article is from the "Xu Big Tree" blog, please be sure to keep this source http://abelxu.blog.51cto.com/9909959/1965630

Java single-instance mode implementation