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Learn the memory management of JVM 03 - Method area and meta space of JVM
2022-07-05 12:15:00 【The king of early rising】
Catalog
What is the method area ?
Used to store... That has been loaded by the virtual machine Type information 、 Constant 、 Static variables 、 Real time compiler compiled code cache and other data .《Java Virtual machine specification 》 Zhongba Method area Described as a logical part of the heap , But it has an alias called “ Non heap ” The purpose is to Java Heap differentiation .
Notice that there is one important place here :《Java Virtual machine specification 》 Zhongba Method area Described as a logical part of the heap , this sentence , Don't be confused . Clear two points :
- Logic
- He's not a pile
Pile up , yes JVM A piece of memory in virtual machine memory , It exists physically , Will be assigned .
Method area , Is a logical part of the heap . Also means that , There is a corresponding Physical implementation .
Implementation of method area
In the early JDK
My early days here JDK The concept is JDK8 Previous .
This is the time , The implementation method area is called Forever .
This permanent generation , yes Java Part of the pile . Type information 、 Constant 、 Data in the method area such as static variables , Stored in this location .
JDK6 When ,HotSopt( A kind of JVM virtual machine ) There is a plan to give up the permanent generation , stay JDK7, Realize the transfer of some data . To JDK8, Completely abandoned the concept of permanent generation .
JDK8
that , Replace the permanent generation . His name is Meta space .
Meta space
This meta space is quite special , It is Local memory A piece of . be not in JVM In the virtual machine .
But be careful : Not everything in the method area is in the meta space .
Constant pool ( Including runtime constant pool and string constant pool ) and Static variables are still in the heap .
Type information ( Metadata information ) And other information is moved to the meta space .
That is, meta space mainly stores type information .
All right. , That's all for the canto .
Keep early hours , take care . King of early rising , I wish you good luck .
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