What Are Runtime Data Areas?

This section describes 6 JVM runtime data areas: Method Area, Heap, Direct Memory, PC Register, JVM Stack and Native Method Stack.

What Are Runtime Data Areas? Here is the definition the JVM specification: "The Java Virtual Machine defines various run-time data areas that are used during execution of a program. Some of these data areas are created on Java Virtual Machine start-up and are destroyed only when the Java Virtual Machine exits. Other data areas are per thread. Per-thread data areas are created when a thread is created and destroyed when the thread exits."

There are 6 JVM data areas divided into 2 categories:

Here a shot description of each JVM runtime data area:

1. Method Area - A thread shared data area that stores per-class structures such as the run-time constant pool, field and method data, and the code for methods and constructors.

2. Heap - A thread shared data area that stores all data objects including both class instances and arrays, except those allocated explicitly in Method Area and Direct Memory area. Objects in heap are allocated when explicitly requested by the application and deallocated by JVM garbage collector automatically.

3. Direct Memory - A thread shared data area that stores buffer objects allocated explicitly in direct memory area. Objects in direct memory are also automatically deallocated by JVM garbage collector.

4. PC (Program Counter) Register - A per-thread data area that contains the address of the instruction currently being executed in the thread. If the method currently being executed is native, the value of the PC register is undefined.

5. JVM Stack - A per-thread data area that stores a stack of frames. Each frame holds local variables and partial results, and plays a part in method invocation and return of the current running method.

6. Native Method Stack - A per-thread data area that stores similar data elements as a JVM stack to execute native (non-Java) methods.

The picture below shows how all 6 JVM runtime data areas are related to each other:
6 JVM Runtime Data Areas

Last update: 2014.

Table of Contents

 About This Book

 Downloading and Installing JDK 1.8.0 on Windows

 Downloading and Installing JDK 1.7.0 on Windows

 java.lang.Runtime Class - The JVM Instance

 java.lang.System Class - The Operating System

 ClassLoader Class - Class Loaders

 Class Class - Class Reflections

 Sun's JVM - Java HotSpot VM

 JRockit JVM 28.2.7 by Oracle Corporation

JVM Runtime Data Areas

What Are Runtime Data Areas?

 Method Area Expansion Demonstration

 OutOfMemoryError on the Method Area

 Method Area Growth with Dynamically Generated Classes

 Garbage Collection Issue with Dynamically Generated Classes

 Interned Strings Stored in Heap

 Heap Expansion Demonstration

 Direct Memory Expansion Demonstration

 allocateMemory() Method on Direct Memory

 JVM Stack Expansion Demonstration

 PC Register and Native Method Stack

 Memory Management and Garbage Collectors

 Garbage Collection Tests

 JVM Stack, Frame and Stack Overflow

 Thread Testing Program and Result

 CPU Impact of Multi-Thread Applications

 I/O Impact of Multi-Thread Applications

 CDS (Class Data Sharing)

 Micro Benchmark Runner and JVM Options

 Micro Benchmark Tests on "int" Operations

 Micro Benchmark Tests on "long" Operations

 Micro Benchmark Tests in JIT Compilation Mode

 Micro Benchmark Tests on "float" and "double" Operations

 Outdated Tutorials


 PDF Printing Version