JVM JDK JRE - The Three Java Big Shots.

   

        
                   JRE ,JVM and JDK are the three Big shots of Java. Without them Java can't go any further than its name. JRE, JVM and JDK are three terms you often heard in relation with Java programming language and most people either confuse between them or think they all are same. In this article , we will learn what is Java Run-time Enviorment(JRE), what is Java virtual Machine (JVM) and what is Java development Kit (JDK) along with Just in Time compiler (JIT).

Once you know what JRE, JVM or JDK means you can differentiate them easily by yourself. Now , we will learn each one of them in detail.

    JRE

• JRE is targeted for execution of Java files. i.e.

                 JRE = JVM + Java Packages Classes(like util,math,lang,etc)+runtime libraries.

• JRE is part of the Java Development Kit(JDK), but can be downloaded separately.
• JRE is also known as Java runtime.
• The Java Runtime Environment (JRE) is a set of programming tools for developing Java applications.The Java Runtime Environment provides the minimum requirements for executing a Java application; it consists of the Java Virtual Machine (JVM), core classes, and supporting files.
• JRE software is available as both a standlone enviorment and a Web browser plug in , which allows Java applets to be run within a Web browser.

JVM

• All language compilers translate source code into machine code for a specific platform.
• Java compiler produces an intermediate code known as bytecode which is a highly optimized set of instructions designed to be executed.
• A Java virtual machine (JVM) is a virtual machine that can execute Java bytecode.
• JVM is the code execution component of the Java platform.
• JVM needs to be implemented for each platform. Once the run-time package exists for a given system , any Java program can run on it.
• Although the details of JVM would differ from platform to platform , but all interpret the same Java bytecode.This helps in acheiving the platform independence feature.
• Sun Microsystems has stated that there are over 5.5 billion JVM-enabled devices.
• For more detailed explanation of JVM :- Click Here

JDK

• JDK is also loosely referred as JRE but its lot more than JRE and it provides all the tools and executable require to compile debug and execute Java Program.
• JDK is also platform specific.
• Current Version of JDK is 1.7 which is also referred as Java7 and it contains javac (java compiler) based on programming rules of Java7 and Java which can execute java7 code with new features like String in Switch, Automatic Resource Management, etc.
• The JDK has the following primary components as its contents:-

1. java - The loader of Java applications. This tool is an interpreter and can interpret the class files generated by the javac compiler.
2. javac- The compiler, which converts source code into Java bytecode.
3. jar - The archiver, which packages related class libraries into a single JAR file.
4. javadoc - The documentation generator , which automatically generates documentation from source code comments.
5. javap - The class file disassembler.
6. appletviewer- This tool can be used to run and debug Java applets without a web browser.
7. javah - The C header and stub generator, used to write native methods.
8. javaws - The Java Web Start Launcher for JNLP (Java Network Launch Protocol) applications.
9. extcheck - This utility can detect JAR-file conflicts.

• For more detailed explanation of JDK : - Click Here

JIT

• JIT is the part of the Java Virtual Machine (JVM) that is used to speed up the execution time.
• 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.

For installation of these three Java BigShots : Click Here