Memory

JRE's memory is segregated into the below parts:

Class (Method) Area

Stores class level data of every class such as the runtime constant pool, field and method data, the code for methods.

Heap Space

Java's Heap Space implementation.

Used to allocate memory to objects at run time

Program Counter Register

• Stores address of currently executing instruction.

  Example: Points to the first line at the start of the program execution

• Also stores address of threads reponsible for executing current instruction

• Size very small

• No effect of Java apps on PC register memory or its content

Stack

Java's implementation of Stack Space.

• Each thread has a private JVM stack created at same time as thread
  • Used to store data and partial results which will be needed while returning value for method and performing dynamic linking
• Stores Stack Frames
• References to objects stored here

Stack Frame

• A new frame is created each time at every invocation of the method.
• Contains all the data for one function call - parameters, return address and its local address
• Stack frame destroyed when method execution completes

Native Method Stack

• Implemented using languages other than Java
• New thread created → Memory allocated in this area
• Size can be fixed or dynamic

References

• How references are stored in Java
• More about layout of java objects — Java Objects Inside Out
• Compressed OOPs

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Children

1. Array
2. Class
3. Methods
4. Objects
5. Static members
6. String

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Backlinks

• Methods (cs)
• Objects (cs)