What is the jvm memory structure and function

JVM memory structure: 1. Program counter; 2. Java virtual machine stack; 3. Local method stack; 4. Heap; 5. Method area. Its functions: 1. Program counter, used to record the address of the next instruction to be executed, which is a private memory area of ​​the thread; 2. Java virtual machine stack, which saves the local variables of the method, part of the results, and the method call and return information. Each thread has its own virtual machine stack. Each method call creates a stack frame to store relevant execution information. The Java virtual machine stack is also private to the thread; 3. Local method stack, etc.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

The memory structure of JVM (Java Virtual Machine) is the basis for running Java programs. The JVM divides memory into different regions, each with its specific functionality and life cycle. The following is a detailed introduction to the JVM memory structure:

1. Program Counter Register: The program counter is used to store the address of the next instruction to be executed. It is a thread-private area, and each thread has an independent program counter. When a thread executes a method, the program counter stores the address of the bytecode instruction being executed by the current thread; when the thread executes a native method, the program counter is empty.

2. Java Virtual Machine Stacks: The Java virtual machine stack is private to the thread, and its life cycle is the same as the thread. Each thread creates a virtual machine stack when it is created, and each method call (including synchronized methods) creates a stack frame to store local variables, operand stacks, dynamic links, and method exit information. Each stack frame corresponds to a method call.

3. Native Method Stacks: The local method stack is used to support the execution of native methods.

4. Heap: The heap is the largest memory area in the JVM and is used to dynamically allocate memory. Heap memory is shared by all threads and is mainly used to store object instances. Heap memory is the main working area of ​​the garbage collector. The garbage collection mechanism automatically recycles no longer used objects and releases heap memory space.

5. Method Area: The method area is used to store class information, constants, static variables and other data that have been loaded by the virtual machine. It is an area shared by all threads. Compared with the heap, the garbage collection efficiency of the method area is lower, mainly because there is less recycling in the constant pool. However, with the development of JIT compiler and the implementation of class data sharing, the recycling efficiency of the method area has also improved.

The above are the five parts of the JVM memory structure. The heap and method area are areas shared by all threads, while the program counter, Java virtual machine stack and local method stack are thread-private areas. These areas play an important role when the JVM runs Java programs:

1. Program counter: is used to record the address of the next instruction to be executed, and is a thread-private memory area.

2. Java virtual machine stack: saves the local variables of the method, part of the results, and the calling and return information of the method. Each thread has its own virtual machine stack, and each method Each call creates a stack frame to store relevant execution information. The Java virtual machine stack is also thread-private.

3. Local method stack: Used to support the execution of native methods.

4. Heap: Heap memory is the largest memory area in the JVM and is mainly used to store object instances. It is an area shared by all threads. The garbage collector will automatically recycle objects that are no longer used and release heap memory space.

5. Method area: Used to store class information, constants, static variables and other data that have been loaded by the virtual machine. It is an area shared by all threads. With the development of JIT compilers and the implementation of class data sharing, the recycling efficiency of method areas has also improved.

These areas play an important role when the JVM runs Java programs. They work together to ensure the normal operation of Java programs.

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