Understanding JDK, JRE and JVM

In Java, the terms JDK, JRE, and JVM refer to different components of the Java ecosystem. Here’s a brief explanation of each:

  1. Java Development Kit (JDK): The JDK stands for software development kit that provides everything you need to develop, compile and run Java programs.
    • JDK= JRE + additional tools like java compiler
  2. Java Runtime Environment (JRE): The JRE is a subset of the JDK that contains only the components necessary to run Java programs.
    • JRE = Java Class Library + JVM (a collection of pre-written code that provides common functionality)
  3. Java Virtual Machine (JVM): The JVM is the core of the Java ecosystem.
    • It is responsible for running Java code by converting bytecode (.class file) into machine-readable code that can be executed by the host operating system.
    • The JVM is also responsible for managing memory and ensuring that Java code runs securely and efficiently.

JVM architecture:

The JVM has several components, including:

  • Class Loader: The class loader is responsible for loading Java classes into the JVM. It searches for classes in the classpath and loads them into memory.
  • Method Area: The method area is a memory region that stores class-level information, such as the names of classes, fields, and methods, and information about the structure of the code.
  • Heap: The heap is a memory region that stores objects and their data. This is where objects are created and garbage collected.
  • Stack: The stack is a memory region that stores information about method invocations and local variables. Each method call creates a new frame in the stack, and the frames are removed when the method returns.
  • PC Register: The PC (Program Counter) register stores the address of the next instruction to be executed.
  • Native Method Stack: The native method stack is used to store information about native methods, which are written in languages other than Java.

In summary,

  • The JDK provides everything you need to develop and run Java programs.
  • The JRE provides the components necessary to run Java programs.
  • The JVM is responsible for executing Java code and managing memory.

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