13 Diagrams Illustrating the Memory Model in Java

Preface

• It is very important to understand the memory area where objects, variables, etc. in Java are stored
• This article will comprehensively explain the memory model & partitioning in the Java virtual machine. I hope you will like it

Directory

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##1. Memory Model & Partition

When the Java virtual machine runs a Java program, it will manage a memory area: the runtime data area

In the runtime data area, it will be divided according to usage:

1. Java virtual machine stack (stack area)
2. Local method stack
3. Java heap (heap area)
4. Method Area
5. Program Counter

## Below, I will introduce each memory model partition in detail

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2. Java堆

简介

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3. Java虚拟机栈

简介

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4. 本地方法栈

Introduction: Very similar to the Java virtual machine stack, but different from the Java virtual machine It lies in: the service object, that is, the Java virtual machine stack serves to execute Java methods; the local method stack serves to execute Native methods

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5. 方法区

简介

注：其内部包含一个运行时常量池，具体介绍如下：

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6. 程序计数器

简介

  

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7. 额外知识：直接内存

• Definition: The channel- and buffer-based I/O method in the NIO class (introduced in JDK1.4) uses the Native function library Directly allocated off-heap memory
• Features: Not limited by heap size

Does not belong to virtual machine runtime data Part of the area & not allocated in the heap

• Application scenario: Suitable for scenarios with frequent calls

Operate through a DirectByteBuffer object stored in the Java heap as a reference to this memory, thereby avoiding copying data back and forth between the Java heap and the Native heap and improving performance

• Exception thrown: OutOfMemoryError, that is, the sum of other memory areas is greater than the physical memory limit

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8. Summary

This article comprehensively explains the memory model & partitioning in JVM, summarized as follows

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