《设计模式解析》 第21章 Singleton 和 Double-checked模式

《设计模式解析》 第21章 Singleton 和 Double-checked模式

Review Questions

Observations

1:	What type of pattern is the Singleton? What general category of pattern does it belong to? 工厂模式
2:	What is the intent of the Singleton pattern? 让对象只初始化一次，并且让其负责自己的状态管理。且能够在全局使用相同的对象。
3:	How many objects is the Singleton responsible for creating? 可以多个对象，但均是单个实例。
4:	The Singleton uses a special method to instantiate objects. What is special about this method? 先判断是否为空，再进行实例化。保证只实例化一次。
5:	What is the difference in when to use the Singleton and Double-Checked Locking patterns? 单线程和多线程的使用。

Interpretations

1:	Is it better to have objects be responsible for handling their own single instantiation than to do it globally for the objects? Why or why not? 自己负责自己的状态管理，这样更易于处理、跟踪等。

Opinions and Applications

1:	Why do you think the Gang of Four call this pattern "Singleton"? Is it an appropriate name for what it is doing? Why or why not? 单例，在运行中，只有一个该类的实例，并且自身能够保证这点。算是名副其实了。
2:	When it was discovered that the Double-Checked Locking pattern as initially described did not work in Java, many people saw it as evidence that patterns were overhyped. I drew exactly the opposite conclusion. Do you agree with this logic? Why or why not? 设计模式只是提供了一种解决问题的范式。具体的实现细节需要根据具体场景进行适应。即使他提出的一些方案在一些场所可能不适应，但我们能够通过他的设计理念，去重新改造，提出适合自己的方案。