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理解 Java 的 GC 与幽灵引用(3)

日期:2011-11-04 点击:127 来源: 未知分享至:

7. 对比

taken from http://mindprod.com/jgloss/phantom.html

8. 小结
一般的应用程序不会涉及到 Reference 编程，但是了解这些知识会对理解 GC 的工作原理以及性能调优有一定帮助, 在实现一些基础性设施比如缓存时也可能会用到，希望本文能有所帮助.

Soft vs Weak vs Phantom References
Type	Purpose	Use	When GCed	Implementing Class
Strong Reference	An ordinary reference. Keeps objects alive as long as they are referenced.	normal reference.	Any object not pointed to can be reclaimed.	default
Soft Reference	Keeps objects alive provided there’s enough memory.	to keep objects alive even after clients have removed their references (memory-sensitive caches), in case clients start asking for them again by key.	After a first gc pass, the JVM decides it still needs to reclaim more space.	java.lang.ref.SoftReference
Weak Reference	Keeps objects alive only while they’re in use (reachable) by clients.	Containers that automatically delete objects no longer in use.	After gc determines the object is only weakly reachable	java.lang.ref.WeakReference java.util.WeakHashMap
Phantom Reference	Lets you clean up after finalization but before the space is reclaimed (replaces or augments the use offinalize())	Special clean up processing	After finalization.	java.lang.ref.PhantomReference

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