Learn JVM garbage collection 02 - a brief introduction to the reference and recycling method area

Catalog  

quote

Strong citation

Soft citation

Weak reference

Virtual reference

Recovery method area

---

quote

In the early JDK in , It's probably described like this ：

If reference The value stored in the data of type represents the starting address of another block of memory , That's right reference Data represents a block of memory 、 A reference to an object .

This definition is very correct , But not enough . In actual operation, there is such a situation .

such as ： An object is to be deleted , But I have enough memory , A little reluctant to , What if it works , Want to keep him . It's not too late to delete when the memory is insufficient .

—— Many of the system's cache functions are in line with such application scenarios .

So ah , four “ tart ” What was born ！！

Strong citation

It refers to the reference assignment that is common in program code ,

It's like Student a = new Student();  This quoting relationship .

As long as I strongly quote in , No garbage collection can help you .

Soft citation

Refers to useful , But not necessarily .

Only objects associated with soft references , In system will happen out of memory Before the exception , These objects will be listed in the recycling scope for a second recycling , If there is not enough memory for this recycle , An out-of-memory exception is thrown .

Weak reference

It is also an unnecessary object to describe . But it will be taken away by garbage collection , No matter whether the memory is enough .

Virtual reference

Also known as “ Ghost quotes ” perhaps “ Phantom reference ”.

This relationship is very nihilistic , It has no effect on the lifetime of the object 、 You can't get object instances through virtual references .

The only purpose is , You can receive a system notification when the object is recycled .

To put it bluntly , That is, when an object is taken away, there can be a movement .

Recovery method area

About the concept of method area , If you don't know, you can see the last link .

According to the concept of method area , Recycling what is stored inside is not profitable . In fact, it's the same .

《Java Virtual machine specification 》 As mentioned in, you don't need virtual machines to implement garbage collection in the method area . Some garbage collectors do not have this part of the design .

Garbage in the method area is mainly discarded constants and types that are no longer used .

This part , That's all .

Study JVM Memory management of 03——JVM Method area of 、 Meta space _ The blog of the early rising King -CSDN Blog What is the method area ？ What is stored in meta space ？https://blog.csdn.net/qq_57014350/article/details/122590237?spm=1001.2014.3001.5501

Keep early hours , take care . The king of early rising wishes you good luck ！