preface

  • To understandJavaThe area of memory where objects, variables, and so on are stored is very important
  • This article will give a comprehensive explanationJavaMemory model & partition in virtual machine, hope you like it

In the coming days, I will publish a series of articles on the JVM, as follows; Interested in sustainable follow Carson_Ho’s Android development notes


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1. Memory model & Partitioning

  • JavaThe VIRTUAL machine is runningJavaA program manages one area of memory: the runtime data area
  • In the runtime data section, it is divided according to usage:
    1. JavaVirtual machine stack (stack area)
    2. Local method stack
    3. JavaHeap (heap area)
    4. Methods area
    5. Program counter


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  • Below, I’ll describe each memory model partition in detail

2. The Java heap

  • Schematic diagram


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  • Introduction to the


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Garbage collection will be explained in an upcoming article

3. Java VM stack

  • Schematic diagram


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  • Introduction to the


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4. Local method stack

  • Schematic diagram


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  • Introduction to the

    Very similarJavaThe vm stack differs from the Java VM in the following aspects: Service object, namely

    Java virtual machine stack for executionJavaMethod service; The local method stack is executionNativeMethods the service

5. Methods area

  • Schematic diagram


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  • Introduction to the


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  • Note that it contains an internal run-time constant pool, described as follows:


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6. Program counter

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  • Introduction to the


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7. Extra knowledge: Direct memory

  • Definition:NIOClass (JDKChannel – and buffer-based in 1.4I/OBy usingNativeOut-of-heap memory allocated directly by the library
  • Features: Not limited by heap size

Not part of the virtual machine run-time data area & not allocated in the heap

  • Application scenario: This mode is applicable to frequently invoked scenarios

A DirectByteBuffer object stored in the Java heap is used as a reference to this memory to avoid copying data back and forth between the Java heap and Native heap and improve performance

  • Exception thrown:OutOfMemoryErrorThat is, the sum with other memory regions is greater than the physical memory limit

8. To summarize

  • This article provides a comprehensive overview of the memory model & partitioning in the JVM, summarized below


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  • In the coming days, I’ll be presenting a series of presentationsJVMArticle, as follows; Interested in sustainable concernsCarson_Ho android Development Notes


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