新手谈设计模式 | 易学教程

单例模式很多都会写面试的时候也经常问于是乎顺手就写了一个

public class Singleton {
	private static Singleton singleton = new Singleton();
	private Singleton(){}
	public static Singleton getSingleton(){
		return singleton;
	}
}

由于这种启动加载，为了减小负载需要延迟加载于是有了

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

确实延迟加载了但如果多线程的话是不是可能出现多个了呢

于是我们考虑线程安全进行加锁

public class Singleton {
	private static Singleton singleton = null;

	private Singleton() {
	}

	public static Singleton getSingleton() {
		synchronized (Singleton.class) {

			if (singleton == null)
				singleton = new Singleton();
		}
		return singleton;
	}

}

但这样一想每次都要来进行锁判断而单例一旦创建了后面就存在了不用进null判断了这样效率是不是还可以提高一点

public class Singleton {
	private static Singleton singleton = null;

	private Singleton() {
	}

	public static Singleton getSingleton() {
		if (singleton == null)
			synchronized (Singleton.class) {

				if (singleton == null)
					singleton = new Singleton();
			}
		return singleton;
	}

}

原来单例也不简单啊，虽然现在自己手写不多很多都用框架来代替了但自己设计一些底层编写时还是会用到

来源：oschina

链接：https://my.oschina.net/u/1584347/blog/672854

标签

单例