What is JDK, JRE and JVM Architecture?

JDK(Java Development Kit):- The Java development kit (JDK) is a software development environment to develop the java applications. It contains Java Run Time Environment (JRE)  and development tools like a compiler (Javac), an interpreter, a document generator (Javadoc) and other tools.

JRE (Java Runtime Environment):- It is the implementation of the JVM. It provides a platform to run the java programs. It consists of the Java Virtual Machine (JVM), core classes and supporting files.

               JRE = JVM +  Library Classes(Java API)

JVM (Java Virtual Machine):- JVM is the main part of the Java language which is responsible for to read the bytecode and execute it.

 JVM performs the following main tasks:

·         Loads code

·         Verifies code

·         Executes code

·         Provides runtime environment

Let’s understand the Architecture of JVM.

ClassLoader: It is a subsystem for loading the class. When we run the java program it first loaded by the classloader.

Class Area: JVM class area stores the class structure like runtime constant pool, field, method data.

Heap: It is a runtime memory area for instance variables, arrays object etc.

Stack: It stores local variables, and it’s partial results. A new frame is created when a method is invoked and it is deleted when this method is complete.

PC register: Program counter register stores address of the Java virtual machine instruction.

Native Method Stack: It contains all native method used in the application. It is a different language instead of java.

Execution Engine: It contains:

Virtual Processor

          Interpreter:- Read bytecode and execute it.

     Just-In-Time Compiler:- It is used to improve the performance of the compiler. It compiles the bytecode hence it reduces the time needed of compilation.

Native Method Interface: The native method interface is a programming framework which provides an interface to communicate with other application written in another language.

Java uses the JNI framework to send output to the console.

Native Method Libraries: It is a collection of the Native Libraries (C, C++) which are needed by the execution engine.