Singleton Pattern 单例模式

单例模式详解

最新推荐文章于 2025-03-16 17:08:38 发布

原创最新推荐文章于 2025-03-16 17:08:38 发布 · 507 阅读

0 ·

CC 4.0 BY-SA版权

Head First Design Patterns 专栏收录该内容

14 篇文章

订阅专栏

本文详细介绍了单例模式的三种实现方式：同步方法、急切创建实例及双重检查锁定，并探讨了每种方法的特点与适用场景。

Singleton Pattern: ensures a class has only one instance, and provides a global point of access to it.

Note: carefully deal with multithreading.

Synchronizing a method can decrease performance by a factor of 100.

1. Synchronize method

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

This has overhead. Lazy create. Only create instance when needed.

2. Eagerly create instance.

public class Singleton {
	private static Singleton uniqueInstance = new Singleton();
	private Singleton(){}
	public static Singleton getInstance() {
		return uniqueInstance;
	}
}

Eager create. Create an instance even it is not used.

3. Use double-checking locking

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

This reduce the synchronize overhead. Use volatile to ensure no cached variable.

应用：设备驱动