JVM memory model parsing

JVM Memory model analysis

Memory structure diagram ：

public class Dome{
    
	public static void main(String[] args){
    
        Student stu = new Student();
        stu.study();
        stu.hash();
        stu = null;
    }
}

stay Dome The whole process of class operation ：

1、Dome Class quilt javac Parsed into bytecode is JVM distinguish

2、 establish main Thread time , It takes up the memory of the virtual machine stack and starts running main Method

3、 If you encounter a class you haven't seen （ for example Dome、Student）, Will continue to call the class loading process , The original information of the class （ The name of the class , Method 、 Inheritance relationships 、 Member variables, etc ） Storage method area

4、new object Student Store in the stack （ Memory size ： Calculate the estimated memory occupied by member variables ）

6、 When calling a method , Required temporary variables 、 Method parameters are stored in the stack frame memory of the virtual machine

7、 When calling a method , The bytecode instruction of the method will be obtained from the method area , The interpreter converts the bytecode into machine code and submits it to CPU perform

8、 When calling a method , The number of instruction lines being executed is stored in the program counter

9、 For virtual machine stacks and local method stacks ,java What is used Oracle Of Hotspot Virtual machines are not divided in detail , Call local method hash The memory of virtual machine stack is also used .

10、 When calling a method , Method called multiple times , The interpreter also calls many times, wasting resources , All hotspot methods will be compiled with an instant compiler

11、 When the object is no longer used , Triggered when out of memory GC Recycling mechanism reclaims heap memory space .

There will be memory overflow

Be careful ： The program counter will not overflow memory

 Throw out OutOfMemoryError error ：
     Heap memory ： When objects are constantly created and occupied 
     Virtual machine stack ： Each thread in the virtual machine stack accounts for 1M Memory , When the number of threads is increasing and running for a long time, it will not be destroyed 
     Method area ： More and more classes are loaded 

 summary ：
	 The method area is mainly responsible for storing the relevant information when the class is loaded 
	 The virtual machine stack is responsible for threads 、 Temporary variable 、 Storage of temporary parameters 
	 Heap is responsible for storing objects 
	 The program counter is responsible for recording the location of the program