单例模式 -- Singleton Pattern
为了避免一个全局使用的类重复的销毁和创建
一、 最简单的单例：
- 新建一个单例的类：
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");
}
}
- 调用示例：
package com.lyx.singleton;
/**
* Created by FollowWinter on 9/29/16.
*/
public class SingletonPattern {
public static void main(String args[]){
Singleton.getInstance().sayHello();
}
}
二、 深入单例：
- 懒汉式-线程不安全
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;
}
}
- 饿汉式-线程安全
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");
}
}
- 双检锁/双重校验锁
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");
}
}
- 登记式、内部静态
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");
}
}
- 枚举
package com.lyx.singleton;
/**
* Created by FollowWinter on 9/29/16.
*/
public enum Singleton5 {
INSTANCE;
public void whateverMethod() {
}
}
三、 单例模式+工厂模式
这么用是因为工厂类总是重复使用，但是没有太大的操作性
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;
}
}
