单例模式

标签：单例模式

1、懒汉式(线程不安全)

public class Singleton {
    private static Singleton instance;
    private Singleton (){}


    public static Singleton getInstance() {
	if (instance == null) {
	    instance = new Singleton();
	}
	return instance;
    }
}

2、懒汉式(线程安全)

public class Singleton {
    private static Singleton instance;
    private Singleton (){}
    public static synchronized Singleton getInstance() {
	if (instance == null) {
	    instance = new Singleton();
	}
	return instance;
    }
}

public class Singleton {
    private static class SingletonHolder {
	private static final Singleton INSTANCE = new Singleton();
    }
    private Singleton (){}
    public static final Singleton getInstance() {
	return SingletonHolder.INSTANCE;
    }
}

4、双重校检锁

public class Singleton {
    private volatile static Singleton singleton;
    private Singleton (){}
    public static Singleton getSingleton() {
	if (singleton == null) {
	    synchronized (Singleton.class) {
		if (singleton == null) {
		    singleton = new Singleton();
		}
	    }
	}
	return singleton;
    }
}

双重校检机制的实现会使用一个关键字volatile，这个关键字的意思是：被volatile修饰的变量的值，将不会被本地线程所缓存，所有对本变量的读写都是直接操作共享内存的，从而确保多个线程可以正确的处理该变量。

单例模式

标签：单例模式

原文地址：http://blog.csdn.net/ivyvae/article/details/41079069