Design pattern-singleton pattern

Singleton pattern

 

 

Singleton pattern): Make sure that a class has only one instance and provides a global access point.

Unit Price Model includesThree parts:Private Constructor,Static variables,Static Method.

 

Specific Method:

1.Standard Singleton Mode:

 

/*** @ Time 2014.6.5 */package singleton;/*** @ author C. l. wang **/public class Singleton {private static Singleton uniqueInstance; // static variable private Singleton () {}// private constructor public static Singleton getInstance () {// static method if (uniqueInstance = null) uniqueInstance = new Singleton (); return uniqueInstance ;}}

2. Consider MultithreadingThree methods:

 

Synchronous (synchronized) Method, AddSynchronized, Will lead to performance degradation, each call example needs to be synchronized, But the use is simple.

 

/*** @ Time 2014.6.5 */package singleton;/*** @ author C. l. wang **/public class Singleton {private static Singleton uniqueInstance; // static variable private Singleton () {}// private constructor public static synchronized Singleton getInstance () {// static method if (uniqueInstance = null) uniqueInstance = new Singleton (); return uniqueInstance ;}}

 

Eager (eagerly) MethodWhen the instance is created at the beginning, the instance space will be occupied when it is not required, that is, the occupied space is too long.

 

/*** @ Time 2014.6.5 */package singleton;/*** @ author C. l. wang **/public class Singleton {private static Singleton uniqueInstance = new Singleton (); // static variable private Singleton () {}// private constructor public static synchronized Singleton getInstance () {// static method // if (uniqueInstance = null) // uniqueInstance = new Singleton (); return uniqueInstance ;}}

Double-checked locking, Use Volatile and synchronized (Singleton. class), Reducing time consumption, applicable Java1.4The above version.

 

 

/*** @ Time 2014.6.5 */package singleton;/*** @ author C. l. wang **/public class Singleton {private volatile static Singleton uniqueInstance; // static variable private Singleton () {}// private constructor public static synchronized Singleton getInstance () {// static method if (uniqueInstance = null) {synchronized (Singleton. class) {if (uniqueInstance = null) uniqueInstance = new Singleton () ;}} return uniqueInstance ;}}

3. Use the single-piece Mode Example:

 

Code:

 

/*** @ Time 2014.6.5 */package singleton;/*** @ author C. l. wang **/public class ChocolateBoiler {// chocolate boiler private boolean empty; private boolean boiled; public static ChocolateBoiler uniqueInstance; // static variable private ChocolateBoiler () {// private constructor empty = true; boiled = false;} public static ChocolateBoiler getInstance () {// static method if (uniqueInstance = null) uniqueInstance = new ChocolateBoiler (); return uniqueI Nstance;} public void fill () {// fill in if (isEmpty () {empty = false; boiled = false;} public void drain () {// dumping if (! IsEmpty () & isBoiled () empty = true;} public void boil () {// cook if (! IsEmpty ()&&! IsBoiled () {boiled = true ;}} public boolean isEmpty () {return empty;} public boolean isBoiled () {return boiled ;}}

4.Enum singleton)Mode to ensure thread security.

Code:

 

/** * @time 2014.6.5 */package singleton;/** * @author C.L.Wang * */public class EnumSingleton {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubeSingleton d1 = eSingleton.INSTANCE;d1.setName(Spike);eSingleton d2 = eSingleton.INSTANCE;d2.setName(Caroline);System.out.println(d1);System.out.println(d2);System.out.println(d1 == d2);}}enum eSingleton {INSTANCE;private String name;public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return [ + name + ];}}

Output:

 

 

[Caroline][Caroline]true