单例模式(Singleton Pattern)_Java

Singleton Pattern

 确保一个类只有一个实例，并提供一个全局访问点

模式一

package com.pattern.singleton;

public class Temp {
	//临时类，用来对比单例模式
}

package com.pattern.singleton;

public class Singleton {
	//私有化构造函数
	private Singleton(){}
	//私有并静态实例
	private static Singleton singleton;
	//提供公有的获取实例的方法
	public static Singleton getInstances(){
		if(singleton==null){
			singleton=new Singleton();
		}
		return singleton;
	}
}

package com.pattern.singleton;

public class Test {

	public static void main(String[] args) {
		Singleton s1=Singleton.getInstances();
		Singleton s2=Singleton.getInstances();
		System.out.println(s1==s2);//true
		
		Temp t1=new Temp();
		Temp t2=new Temp();
		System.out.println(t1==t2);//false
	}
}

模式二

package com.pattern.singleton;
/**
 * 这种单例模式是先创建一份实例，需要的话直接使用即可
 */
public class Singleton2 {
	private Singleton2(){}
	private static Singleton2 singleton=new Singleton2();
	public static Singleton2 getInstances(){
		return singleton;
	}
}

 多线程情况下的单例模式

package com.pattern.singleton;

public class ThreadSingleton {
	//私有化构造函数
	private ThreadSingleton(){}
	//私有并静态实例
	private static ThreadSingleton singleton;
	//提供公有,线程安全的获取实例的方法
	public static synchronized ThreadSingleton getInstances(){
		if(singleton==null){
			singleton=new ThreadSingleton();
		}
		return singleton;
	}
}