《設計模式解析》 第21章 Singleton 和 Double-checked模式

《設計模式解析》 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? 工廠模式
2:	What is the intent of the Singleton pattern? 讓對象只初始化一次，並且讓其負責自己的狀態管理。且能夠在全局使用相同的對象。
3:	How many objects is the Singleton responsible for creating? 可以多個對象，但均是單個實例。
4:	The Singleton uses a special method to instantiate objects. What is special about this method? 先判斷是否爲空，再進行實例化。保證只實例化一次。
5:	What is the difference in when to use the Singleton and Double-Checked Locking patterns? 單線程和多線程的使用。

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? 自己負責自己的狀態管理，這樣更易於處理、跟蹤等。

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? 單例，在運行中，只有一個該類的實例，並且自身能夠保證這點。算是名副其實了。
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? 設計模式只是提供了一種解決問題的範式。具體的實現細節需要根據具體場景進行適應。即使他提出的一些方案在一些場所可能不適應，但我們能夠通過他的設計理念，去重新改造，提出適合自己的方案。