單例模式 -- Singleton Pattern
為了避免一個(gè)全局使用的類重復(fù)的銷毀和創(chuàng)建
一、 最簡單的單例：
- 新建一個(gè)單例的類：
package com.lyx.singleton;
/**
* Created by FollowWinter on 9/29/16.
*/
public class Singleton {
private static Singleton singleton=new Singleton();
private Singleton(){}
public static Singleton getInstance() {
return singleton;
}
public void sayHello(){
System.out.println("Hello Singleton");
}
}
- 調(diào)用示例：
package com.lyx.singleton;
/**
* Created by FollowWinter on 9/29/16.
*/
public class SingletonPattern {
public static void main(String args[]){
Singleton.getInstance().sayHello();
}
}
二、 深入單例：
- 懶漢式-線程不安全
package com.lyx.singleton;
/**
* Created by FollowWinter on 9/29/16.
*/
public class Singleton2 {
private static Singleton2 singleton;
private Singleton2(){};
public static Singleton2 getInstance() {
if (singleton==null){
singleton=new Singleton2();
}
return singleton;
}
}
- 餓漢式-線程安全
package com.lyx.singleton;
/**
* Created by FollowWinter on 9/29/16.
*/
public class Singleton3 {
private static Singleton3 singleton=new Singleton3();
private Singleton3(){}
public static synchronized Singleton3 getInstance() {
return singleton;
}
public void sayHello(){
System.out.println("Hello Singleton");
}
}
- 雙檢鎖/雙重校驗(yàn)鎖
package com.lyx.singleton;
/**
* Created by FollowWinter on 9/29/16.
*/
public class Singleton4 {
private volatile static Singleton4 singleton=new Singleton4();
private Singleton4(){}
public static synchronized Singleton4 getInstance() {
if (singleton == null) {
synchronized (Singleton4.class) {
if (singleton == null) {
singleton = new Singleton4();
}
}
}
return singleton;
}
public void sayHello(){
System.out.println("Hello Singleton");
}
}
- 登記式、內(nèi)部靜態(tài)
package com.lyx.singleton;
/**
* Created by FollowWinter on 9/29/16.
*/
public class Singleton4 {
private static class SingletonHolder {
private static final Singleton4 INSTANCE = new Singleton4();
}
private Singleton4() {
}
public static final Singleton4 getInstance() {
return SingletonHolder.INSTANCE;
}
public void sayHello() {
System.out.println("Hello Singleton");
}
}
- 枚舉
package com.lyx.singleton;
/**
* Created by FollowWinter on 9/29/16.
*/
public enum Singleton5 {
INSTANCE;
public void whateverMethod() {
}
}
三、 單例模式+工廠模式
這么用是因?yàn)楣S類總是重復(fù)使用，但是沒有太大的操作性
package com.lyx.factory;
import com.lyx.singleton.Singleton;
/**
* Created by FollowWinter on 9/29/16.
*/
public class SingletonShapFactory {
private static SingletonShapFactory singletonShapFactory=new SingletonShapFactory();
private SingletonShapFactory(){};
public static SingletonShapFactory getInstance() {
return singletonShapFactory;
}
}
