Shulou(Shulou.com)06/01 Report--

Editor to share with you there are several types of run-time data areas in JVM, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's learn about it!

When JVM runs a java program, it divides the memory it manages into the runtime data areas shown in the figure. Roughly divided into two types of memory space:

Thread data shared memory areas that are created and destroyed as JVM processes start and stop

An area of thread private data memory that is created and destroyed with thread creation and harness.

Note: there is a description of the method area above. In fact, the method area is standard and always exists. The so-called permanent generation or metadata space is only the implementation of the method area. After the JDK1.8 version, the permanent generation in the hotspot method area has been replaced by the metadata space, and the heap memory space is no longer used and moved directly to local memory.

Personally, I think the reasons for removing the permanent generation from the heap are:

1. There is an official explanation in http://openjdk.java.net/jeps/122. It is recommended that the metadata of the class be put into local memory, and the constant pool and declaration variables should be placed in the heap. Because the recovery effect of the class is not obvious, putting it in the heap will increase the number of GC.

2. Compatible with other virtual machines, JRockit and J9 virtual machines have never been implemented forever.

That's all of the article "there are several types of runtime data areas in JVM". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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