Shulou(Shulou.com)06/03 Report--

This article mainly introduces "the understanding and use of Java weak citation". In daily operation, I believe many people have doubts about the understanding and use of Java weak citation. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about "the understanding and use of Java weak citation". Next, please follow the editor to study!

In Java, when an object o is created, it is placed in the Heap. When GC is running, if no reference is found to o, o will be recycled to free up memory space. Or in other words, when an object is reclaimed, two conditions must be met: 1) there are no references to it. 2) GC is run.

When writing code in the real world, we tend to make sure that the object is recycled the next time the GC runs by leaving all the referece pointing to the object empty (you can use java-verbose:gc to observe the behavior of the gc)

Object c = new Car ()

C=null

However, manually emptying objects is tedious for programmers and runs counter to the concept of automatic recycling. For simple cases, there is no need for programmers to do manual null, because in java, for simple objects, when the method that called it is executed, the reference to it is popup from stack, so it can be recycled the next time GC executes.

However, there are special exceptions. When using cache, because the object of cache is exactly what the program needs to run, the reference in cache will not be given by GC as long as the program is running (that is, the reference in cache has the same life cycle as the main program). So with more and more reference in cache, more and more object cannot be recycled by GC and cannot be recycled automatically. When the object needs to be recycled, the task of recycling the object is left to the programmer. However, this goes against the nature of GC (automatic recycling of recyclable objects).

Therefore, weak reference is introduced into java. Compared to the strong reference in the previous example:

Object c = new Car (); / / as long as c still points to car object, car object will not be recycled

When an object is pointed only by weak reference and no other strong reference points, if GC runs, the object will be recycled. The syntax of weak reference is:

WeakReference weakCar = new WeakReference (Car) (car)

When you want to get the object referenced by weak reference, you first need to determine whether it has been reclaimed:

WeakCar.get ()

If this method is empty, the object pointed to by weakCar has been recycled.

At this point, the study on "the understanding and use of Java weak citations" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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