Weak references in Java

Strong references

StringBuffer buffer = new StringBuffer();

Normal object creation is this type, and as long as buffer exists, the object will not be recycled by GC. It can also cause some problems, such as: When you add a handle to a hashmap, they don't automatically clear the cache of a picture when they are saved.

Weak references

referencequeue<string> WRQ = new referencequeue<string> ();
weakreference<string> ws = new weakreference<string> (s2, WRQ);

A weak reference cannot prevent the GC from reclaiming the memory that its object points to, and all of the Times by Handle.get () returns NULL. There is a dedicated weakhashmap that prevents the collection of objects because of the presence of keys. Storage for collections

Soft references

referencequeue<string> SRQ = new referencequeue<string> ();
softreference<string> ss = new softreference<string> (s1, SRQ);

Only when the memory is not enough to be recycled in weak reference, does not cause oom, so it is suitable for caching

Phantom references

referencequeue<string> PRQ = new referencequeue<string> ();
phantomreference<string> PS = new phantomreference<string> (S3, PRQ);

WeakReference is to put the handle into the Rference Queue before the GC, which can theoretically be resurrected in finalized. Phantom reference will only be placed in the reference queue after the object is retracted

Can be used to flag when an object is destroyed, or to ensure that the object is not resurrected in GC.

Reference:

Http://docs.oracle.com/javase/7/docs/api/java/util/WeakHashMap.html

Https://community.oracle.com/blogs/enicholas/2006/05/04/understanding-weak-references

Http://my.oschina.net/sulliy/blog/482101

Weak references in Java