【设计模式】之实例化单例模式

com.cleversoft.designpatterns.singleton1.Singleton.java:

package com.cleversoft.designpatterns.singleton1;

/** *//**

* Hungry Singleton

*

*/

public class Singleton {

private static Singleton singleton = new Singleton();

private Singleton() {

}

public static Singleton getInstance() {

return singleton;

}

public String demoMethod() {

return "This is a hungry singleton demo!";

}

}

//---------------------------------------------------------------------------------------------------------

com.cleversoft.designpatterns.singleton1.Main.java:

package com.cleversoft.designpatterns.singleton1;

public class Main {

/** *//**

* @param args

*/

public static void main(String[] args) {

// TODO Auto-generated method stub

System.out.println(Singleton.getInstance().demoMethod());

}

}

//---------------------------------------------------------------------------------------------------------

懒汉式单例

com.cleversoft.designpatterns.singleton2.LazySingleton.java:

package com.cleversoft.designpatterns.singleton2;

/** *//**

* Lazy Singleton

*

*/

public class LazySingleton {

static boolean instance_flag = false;

private LazySingleton() {

}

synchronized public static LazySingleton getInstance() {

if (!instance_flag) {

instance_flag = true;

return new LazySingleton();

} else

return null;

}

}

//---------------------------------------------------------------------------------------------------------

com.cleversoft.designpatterns.singleton2.Main.java:

package com.cleversoft.designpatterns.singleton2;

public class Main {

/** *//**

* @param args

*/

public static void main(String[] args) {

// TODO Auto-generated method stub

LazySingleton ls1, ls2;

System.out.println("Start to get first Instance");

ls1 = LazySingleton.getInstance();

if (ls1 != null){

System.out.println("This is the first Instance!/n");

}

System.out.println("Start to get second Instance");

ls2 = LazySingleton.getInstance();

if (ls2 != null){

System.out.println("This is the second Instance!");

}

else{

System.out.println("You can just get 1 Instance!");

}

}

}

引用：

>强烈建议大家不要再花时间在实现双重检查成例上

是这样，不必在这上面钻牛角尖，而且单例模式在实际应用中已经逐步被Ioc容器替代，实用价值不高。

有上限多例模式

com.cleversoft.designpatterns.multiton.Die.java:

package com.cleversoft.designpatterns.multiton;

import java.util.Random;

import java.util.Date;

public class Die {

private static Die die1 = new Die();

private static Die die2 = new Die();

private Die() {

}

public static Die getInstance(int whichOne) {

if (whichOne == 1) {

return die1;

} else {

return die2;

}

}

public synchronized int dice() {

Date d = new Date();

Random r = new Random(d.getTime());

int value = r.nextInt();

value = Math.abs(value);

value = value % 6;

value += 1;

System.out.println(value);

return value;

}

}

//---------------------------------------------------------------------------------------------------------

com.cleversoft.designpatterns.multiton.Main.java:

package com.cleversoft.designpatterns.multiton;

public class Main {

private static Die die1;

private static Die die2;

public static void main(String[] args) {

die1 = Die.getInstance(1);

die2 = Die.getInstance(2);

die1.dice();

die2.dice();

}

}

无上限多例模式

比较合适的例子就是在应用程序中的“多语言支持”和序列键生成器。