What Is Java, JVM, JRE and JDK?

This section describes what is Java, what is JVM (Java Virtual Machine), also called JRE (Java Runtime Environment), and what is JDK (Java Development Kit).

What Is Java? Java is a general-purpose programming language that was developed by Sun Microsystems. Java applications are typically compiled to bytecode (class file) that can run on any Java virtual machine (JVM) regardless of computer architecture.

What Is JVM? JVM (Java Virtual Machine) is a system application that installed on a specific computer architecture and operating system to run Java programs compiled in bytecode format.

JVM is also called JRE (Java Runtime Environment).

What Is JDK? JDK (Java Development Kit) is a development tool that allows you to compile and debug applications.

Here is a very simple program called Hello.java written in Java language:

class Hello {
   public static void main(String[] a) {
      System.out.println("Hello world!"); 	
   }
}

If you have JDK 7 installed on your Windows system, you can use the "javac" command in JDK to compile the above Java program like this:

C:\>\progra~1\java\jdk1.7.0_07\bin\javac Hello.java

If you have JVM (JRE) 7 installed on your Windows system, you can use the "java" command in JVM to run the compiled Java program like this:

C:\>\progra~1\java\jre7\bin\java Hello
Hello world!

Last update: 2013.

Table of Contents

 About This Book

 Introduction to Microsoft Windows

 Introduction to Windows Explorer

 Introduction to Internet Explorer

 "Paint" Program and Computer Graphics

 GIMP - GNU Image Manipulation Program

 JPEG Image File Format Quality and Size

 GIF Image File Format and Transparent Background

 "WinZip" - ZIP File Compression Tool

 "WinRAR" - RAR and ZIP File Compression Tool

 FTP Server, Client and Commands

 "FileZilla" - Free FTP Client and Server

 Web Server Log Files and Analysis Tool - "Analog"

 Spyware Adware Detection and Removal

 IE Addon Program Listing and Removal

 Vundo (VirtuMonde/VirtuMundo) - vtsts.dll Removal

 Trojan and Malware "Puper" Description and Removal

 VSToolbar (VSAdd-in.dll) - Description and Removal

 Spybot - Spyware Blocker, Detection and Removal

 Setting Up and Using Crossover Cable Network

 Home Network Gateway - DSL Modem/Wireless Router

 Windows Task Manager - The System Performance Tool

 "tasklist" Command Line Tool to List Process Information

 "msconfig" - System Configuration Tool

 Configuring and Managing System Services

 Windows Registry Key and Value Management Tools

 Startup Programs Removal for Better System Performance

 Winsock - Windows Sockets API

Java on Windows

What Is Java, JVM, JRE and JDK?

 Managing JVM and JDK

 Removing "Java Update - jusched.exe"

 Glossary of Terms

 Outdated Tutorials

 References

 PDF Printing Version