DesignPattern_Java:SingletonPattern

单例模式 SingletonPattern

Ensure a class has only one instance,and provide a global point of access to it.

单例模式的主要作用是确保一个类只有一个实例存在。

懒汉式单例类：第一次引用类时，才进行对象实例化。

package com.DesignPattern.Creational.Singleton;

public class Singleton_lHan {

private static Singleton_lHan _instance = null;

private Singleton_lHan() {
}

synchronized public static Singleton_lHan getInstance() {
if (_instance == null) {
_instance = new Singleton_lHan();
}
return _instance;
}
}


饿汉式单例类：类加载时，就进行对象实例化。

package com.DesignPattern.Creational.Singleton;

public class Singleton_eHan {

private static Singleton_eHan m_instance = new Singleton_eHan();

private Singleton_eHan() {
}

public static Singleton_eHan getInstance() {
return m_instance;
}
}


单例模式的实例
创建一个饿汉式单例类:GlobalNum.java

package com.DesignPattern.Creational.Singleton;

public class GlobalNum {

private static GlobalNum gn = new GlobalNum();
private int num = 0;

public static GlobalNum getInstance() {
return gn;
}

public synchronized int getNum() {
return ++num;
}
}


SingleDemo.java
package com.DesignPattern.Creational.Singleton;

public class SingleDemo {

//测试单例模式
public static void main(String[] args) {
//创建线程A
NumThread threadA = new NumThread("thread A");
//创建线程B
NumThread threadB = new NumThread("thread B");
//启动线程
threadA.start();
threadB.start();

}
}
//线程类
class NumThread extends Thread {

private String threadName;

public NumThread(String name) {
threadName = name;
}

//重写线程的run方法(线程任务)
public void run() {
GlobalNum gnObj = GlobalNum.getInstance();
//循环访问，输出访问次数
for (int i = 0; i < 5; i++) {
System.out.println(threadName + "第" + gnObj.getNum() + "次访问!");
try {
this.sleep(1000); //线程休眠1000毫秒
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

}