Form of objects in memory & memory allocation mechanism

One 、 Object exists in memory in form

1、 First , The memory is divided into three parts ： Stack , Pile up , Method area .

• Stack ： The reference used to store the object and the method run here .
  Be careful ：

1. When the method runs, it will enter the stack , Immediately after the method is finished .
2. After method stack , All object variables in this method will be recycled .

• Pile up ： Used to store everything new Objects created .（ Address of the object , Object properties, member variables, etc ）

Method area ： Used to store information about classes （ attribute 、 Method ）, And constant pools .
Only constants of string type are stored in the constant pool .（ For example, in the heap , The attribute type is of string type , Do not store values directly , But the storage address , This address is the address of the corresponding value in the constant pool .）

• Views on whether the constant pool exists in the heap or in the method area .
  JDK1.8 String constant pool and runtime constant pool belong to method area logically , But it's actually in heap memory , Therefore, it can be said that both are stored in the heap , It can also be said that two exist in the method area , This is what is easy to misunderstand .
  

Two 、 Memory allocation mechanism for classes and objects

First look at the following code

Person p1 = new Person();
p1.age = 10;
p1.name = " Xiao Ming ";
Person p2 = p1;// hold p1 Given to p2   Give Way p2 Point to p1
System.out.println(p2.age);

Excuse me, ：p2.age How much is it ？ And draw the memory map （ Suppose an address ）

Java Memory structure analysis
1) Stack ： General storage of basic data types ( local variable )
2) Pile up ： Storage objects (Cat cat , Array etc. )
3) Method area ： Constant pool ( Constant , Like strings ), Class loading information