java-design mode-Singleton mode-a hungry man mode, lazy mode

//-------------------------------------------------------------A hungry man mode--start------------------------------------------------ ----------- PackageCom.study.DesignPattern01;/*** Create a single instance of a Hungry man mode *@authorZlhome * Some objects, we only need one, if more, then it can lead to inconsistent data, excessive resources and so on, such as: Configuration file, tool class, thread pool, cache, log Object*/ Public classSingleton {//1, the construction method of privatization (such a class can not be instantiated)    PrivateSingleton () {System.out.println ("Instantiating the Singleton class"); }        //2, instantiate a singleton object, the object is static (so it will only be instantiated once), private (security, external cannot directly singleton.instance call)    Private StaticSingleton instance =NewSingleton (); //3, provide a static method (static method, the class can be called directly), to obtain a singleton     Public StaticSingleton getinstance () {returninstance; }}//--------------------------------------------------------------------------------------------- PackageCom.study.DesignPattern01;ImportOrg.junit.After;ImportOrg.junit.AfterClass;ImportOrg.junit.Before;ImportOrg.junit.BeforeClass;Importorg.junit.Test; Public classsingletontest {@BeforeClass Public Static voidSetupbeforeclass ()throwsException {System.out.println ("JUnit begins Beforeclass ..."); } @AfterClass Public Static voidTeardownafterclass ()throwsException {System.out.println ("JUnit after Afterclass ..."); } @Before Public voidSetUp ()throwsException {System.out.println ("JUnit begins before ..."); } @After Public voidTearDown ()throwsException {System.out.println ("JUnit after ..."); } @Test Public voidTest () {System.out.println ("JUnit begins ..."); Singleton instance=singleton.getinstance (); Singleton Instance1=singleton.getinstance (); System.out.println ("Is equal:" + (instance==Instance1)); }}//-------------------------------------------------------------A hungry man mode-end------------------------------------------------ -----------//============================================================ Lazy Mode-Start ======================================= ===================== PackageCom.study.DesignPattern01; Public classSingleton1 {//1. Set the construction method to private (so that the class cannot be instantiated externally)    PrivateSingleton1 () {System.out.println ("Instantiating Singleton1"); }        //2, affirm the single Case object    Private StaticSingleton1 instance; //3. Provide a static method (static method belongs to class) for external invocation     Public StaticSingleton1 getinstance () {if(instance==NULL) {System.out.println ("Instantiating Singleton1 objects for the first time"); Instance=NewSingleton1 (); }        returninstance; }}//============================================================ PackageCom.study.DesignPattern01;ImportOrg.junit.After;ImportOrg.junit.AfterClass;ImportOrg.junit.Before;ImportOrg.junit.BeforeClass;Importorg.junit.Test; Public classsingleton1test {@BeforeClass Public Static voidSetupbeforeclass ()throwsException {System.out.println ("JUnit begins Beforeclass ..."); } @AfterClass Public Static voidTeardownafterclass ()throwsException {System.out.println ("JUnit after Afterclass ..."); } @Before Public voidSetUp ()throwsException {System.out.println ("JUnit begins before ..."); } @After Public voidTearDown ()throwsException {System.out.println ("JUnit after ..."); } @Test Public voidTest () {System.out.println ("JUnit begins ..."); Singleton1 instance=singleton1.getinstance (); Singleton1 Instance1=singleton1.getinstance (); System.out.println ("Is equal:" + (instance==Instance1)); }}//============================================================ Lazy mode-end ======================================= =====================

Design Patterns
Higher reliability, easier understanding, better scalability ' easier to maintain
1. Single Case mode:
1) Single case background, situation:
Some objects, we only need one, if more, then it can lead to inconsistent data,
Take up too much resources and so on, such as:
Configuration files, tool classes, thread pools, caches, log objects
2) Principle:
Instantiating an object is implemented by constructing a method (the program class is not written, the program class has a default constructor),
The singleton allows only one instance to be obtained, so

A Hungry man mode:
Instantiate object when class is loaded (hungry, active instance object)
(1) The implementation of a single example to rewrite the construction method: The construction method is rewritten as private, after rewriting, it can not be directly instantiated (not allowed to create an instance directly outside)
(2) Create a unique instance of the class (the class goes to the new instance, and the instance is a static[variable, the method adds the static and then becomes the class all, not the instance object must be created to invoke], so that the instance can be called directly from the class [class name. Instance variable name])
(3) For the sake of security, external direct access to member variables is not allowed, so (2) it needs to be optimized to make the static instance of a class private, and then it cannot be accessed directly after the class name. Instance variable name, so provide a method of the class get, The Get method of the class also needs to be static to be called by the class name. Method Name.

Lazy mode:
Class loading is just a declaration, the invocation of the Singleton when the instantiation (lazy, not active to the instance object)
(1) Declare a singleton, and not instantiate a singleton object
(2) in the Get method to judge, if there is no instance of the object, the singleton object is instantiated and returned

Contrast:
Lazy mode: Class loading fast, getting objects slow, thread-safe
A Hungry man mode: class loading slow, getting objects fast, thread insecure

Summary: Static modified variables, method data classes, can be directly called through the class

java-design mode-Singleton mode-a hungry man mode, lazy mode