JVM four reference types

One 、 Strong citation ：

natural new When an object is referred to, it is a strong reference . You can manipulate objects directly by reference .gc Objects pointed to by strong references will not be recycled , Unless the reference is equal to null

Two 、 Soft citation

new Out SoftReference Nest other objects in its construction method

1、m Point to sr Strong citation ,sr Object points to byte array soft reference . Every time gc It will not actively clean up soft references , Only when there are other strong references , And if the space in the heap area is insufficient, it will be cleared . You can quote .get Method to get nested objects

2、 effect ： Used to cache , Set some frequently used as soft references （ Give Way SoftReference Nesting things to be used in ）, So it won't be gc Recycle , Can be used often . And when there is not enough memory , It can be killed by other strong references at any time

3、 ... and 、 Weak reference

new Out WeakReference Nest other objects in its construction method

1、 Memory diagram as above . As long as garbage collection starts, it will be recycled . You can quote .get Method to get nested objects

2、 effect ： stay ThreadLocal To prevent memory leakage （ See the multi threading column ThreadLocal）

Four 、 Virtual reference

new Out PhantomReference Nest other objects in its construction method

You have to add a queue , Because every time I was returned