JVM,JDK,JRE and JVM Architecture

 Translator

Translator is a program that converts a computer program into machine  language.

There are 3 types of Translator

  1. Interpreter:-Interpreter translates line by line program

  2. Compiler:-Compiler translates all lines of a program at single time

  3. Assembler:-Assembler  translates Assembly language to machine  language.

  • Source code :-Developer written Program  eg.add.java
  • Compiled Code:- Compiler generated  Program eg.add.class
  • Executable Code:-OS understandable readily executable Program

JRE(Java Runtime Environment)
  • JRE is an acronym for Java Runtime Environment. 
  • It is also written as Java RTE. The Java Runtime Environment is a set of software tools which are used for developing Java applications. 
  • It is used to provide the runtime environment. It is the implementation of JVM. 
  • It physically exists. It contains a set of libraries + other files that JVM uses at runtime.
  • The implementation of JVM is also actively released by other companies besides Sun Micro Systems.

JDK(Java Development Kit.)

  • JDK is an acronym for Java Development Kit.

  • The Java Development Kit (JDK) is a software development environment which is used to develop Java applications and applets. It physically exists. It contains JRE + development tools.

JDK is an implementation of any one of the below given Java Platforms released by Oracle Corporation:

  • Standard Edition Java Platform

  • Enterprise Edition Java Platform

  • Micro Edition Java Platform

The JDK contains a private Java Virtual Machine (JVM) and a few other resources such as an interpreter/loader (java), a compiler (javac), an archive (jar), a documentation generator (Javadoc), etc. to complete the development of a Java Application.

JVM (Java Virtual Machine) 

JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime environment in which java bytecode can be executed.

JVMs are available for many hardware and software platforms (i.e. JVM is platform dependent).

  1. A specification where working of Java Virtual Machine is specified. But implementation provider is independent to choose the algorithm. Its implementation has been provided by Oracle and other companies.
  2. An implementation Its implementation is known as JRE (Java Runtime Environment).
  3. Runtime Instance Whenever you write java command on the command prompt to run the java class, an instance of JVM is created.

The JVM performs following operation:

  • Loads code
  • Verifies code
  • Executes code
  • Provides runtime environment

JVM provides definitions for the:

  • Memory area
  • Class file format
  • Register set
  • Garbage-collected heap
  • Fatal error reporting etc.
 
JVM (Java Virtual Machine) Architecture

1) Classloader

Classloader is a subsystem of JVM which is used to load class files. Whenever we run the java program, it is loaded first by the classloader. There are three built-in classloaders in Java.

  1. Bootstrap ClassLoader: This is the first classloader which is the super class of Extension classloader. It loads the rt.jar file which contains all class files of Java Standard Edition like java.lang package classes, java.net package classes, java.util package classes, java.io package classes, java.sql package classes etc.
  2. Extension ClassLoader: This is the child classloader of Bootstrap and parent classloader of System classloader. It loades the jar files located inside $JAVA_HOME/jre/lib/ext directory.
  3. System/Application ClassLoader: This is the child classloader of Extension classloader. It loads the classfiles from classpath. By default, classpath is set to current directory. You can change the classpath using "-cp" or "-classpath" switch. It is also known as Application classloader.

2) Class(Method) Area

Class(Method) Area stores per-class structures such as the runtime constant pool, field and method data, the code for methods.

3) Heap

It is the runtime data area in which objects are allocated.

4) Stack

Java Stack stores frames. It holds local variables and partial results, and plays a part in method invocation and return.

Each thread has a private JVM stack, created at the same time as thread.

A new frame is created each time a method is invoked. A frame is destroyed when its method invocation completes.

5) Program Counter Register

PC (program counter) register contains the address of the Java virtual machine instruction currently being executed.

6) Native Method Stack

It contains all the native methods used in the application.

7) Execution Engine

  1. A virtual processor
  2. Interpreter: Read bytecode stream then execute the instructions.
  3. Just-In-Time(JIT) compiler: It is used to improve the performance. JIT compiles parts of the byte code that have similar functionality at the same time, and hence reduces the amount of time needed for compilation. Here, the term "compiler" refers to a translator from the instruction set of a Java virtual machine (JVM) to the instruction set of a specific CPU.

8) Java Native Interface

Java Native Interface (JNI) is a framework which provides an interface to communicate with another application written in another language like C, C++, Assembly etc. Java uses JNI framework to send output to the Console or interact with OS libraries.


Difference between C Compiler and Java Compiler



Comments

Post a Comment

Popular posts from this blog

Polymorphism in Java

Image
  Polymorphism in Java:- The word polymorphism means having many forms. In simple words, we can define polymorphism as the ability of a message to be displayed in more than one form.  Polymorphism is considered as one of the important features of Object Oriented Programming.  Polymorphism allows us to perform a single action in different ways.  In other words, polymorphism allows you to define one interface and have multiple implementations. The word “poly” means many and “morphs” means forms, So it means many forms. Two type of  polymorphism in java:- 1.Compile time Polymorphism 2. Polymorphism  Compile time polymorphism:- It is also known as static polymorphism.  This type of polymorphism is achieved by function overloading or operator overloading. Overloading and overriding:- Method Overloading:- When there are multiple functions with same name but different parameters then these functions are said to be o verloaded .  Functions can be overloaded by change in number of arguments or
Read more

Java Introduction

Java Introduction  :- -Java is called as programming language because by using Java, we can write programs. -Java is created in 1995. -Java is a programming language, platform & technology. -Java was originally developed by James Gosling at Sun Microsystems (which has since been acquired by Oracle) and released in 1995 as a core component of Sun Microsystems' Java platform. -It is owned by Oracle , and more than 3 billion devices run Java. List of programming languages: C, C++, Java, Python, VC++, Visual Basic.Net, C#.Net, Small talk, Simula, Ada, etc., Top 5 programming languages:- Java, C, Python, C++ & C# C & C++ are popular for developing system  software Java popular for developing Internet Applications Python popular for developing Artificial Intelligence Applications C# popular for developing Graphical User Interface Applications History of Java:-           The history of Java is very interesting. Java was originally designed for interactive television, (but it
Read more

Applet life cycle

  Applet Life Cycle in Java In Java, an  applet  is a special type of program embedded in the web page to generate dynamic content. Applet is a class in Java. The applet life cycle can be defined as the process of how the object is created, started, stopped, and destroyed during the entire execution of its application. It basically has five core methods namely init(), start(), stop(), paint() and destroy().These methods are invoked by the browser to execute. Along with the browser, the applet also works on the client side, thus having less processing time. Methods of Applet Life Cycle init():  The init() method is the first method to run that initializes the applet. It can be invoked only once at the time of initialization. The web browser creates the initialized objects, i.e., the web browser (after checking the security settings) runs the init() method within the applet. start():  The start() method contains the actual code of the applet and starts the applet. It is invoked immediate
Read more