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Posts Tagged ‘JDK 1.5’

Java Terminologies

September 6, 2009 Leave a comment

 

Few terminologies to be familiar with, before getting started with Java:

 

Java Platform:

The Java platform from Sun allows developing and running programs written in the Java programming language. The platform is not specific to any one processor or operating system, but rather an execution engine called virtual machine and a compiler with a set of standard libraries that are implemented for various hardware and operating systems so that Java programs can run identically on all of them.

The Java Platform consists of several programs, each of which provides a distinct portion of its overall capabilities. For example, the Java compiler converts Java source code into Java byte-code, an intermediate language to be executed by the virtual machine (JVM) and it is provided as part of the Java Development Kit (JDK). The Java Runtime Environment (JRE), complementing the JVM with a just-in-time (JIT) compiler, converts intermediate byte-code into native machine code on the fly. Also supplied are extensive libraries, pre-compiled in which are several other components, some available only in certain versions.

The essential components in the platform are the Java language compiler, the libraries, java language itself (Java API) and the runtime environment in which Java intermediate byte-code “executes” according to the rules laid out in the virtual machine specification. 

  Java Platform

JVM:

The heart of the Java Platform is the concept of a “virtual machine” that executes Java byte-code. This byte-code is the same no matter what hardware or operating system the program is running under. The use of byte-code as an intermediate language permits Java programs to run on any platform that has a virtual machine available. Although Java programs are platform independent, the code of the Java Virtual Machine (JVM) that execute these programs is not so every supported operating platform has its own JVM.

The JVM is a crucial component of the Java Platform. It is a platform-independent execution environment that converts Java byte-code into machine language and executes it. Most programming languages compile source code directly into machine code that is designed to run on a specific microprocessor architecture or operating system, such as Windows or UNIX.

The JVM is an instance of the JRE (Java Runtime Environment) and comes into action when a Java program is executed. JVM can be obtained with JRE / JDK distribution.

Few functionalities of JVM are:-

  • Loading of class files (compiled java source code).
  • Verification of class files i.e., Class files should contain valid byte-code.
  • Interpretation of byte code and then run the program. 

  

JIT: Read more…

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Java Installation & Configuration

August 18, 2009 4 comments

 

 

Java is freely downloadable from Sun’s website (http://developers.sun.com/downloads/) . What’s to decide is which version to chose? At the time of this post, recommended Java versions are 1.4 , 1.5 and 1.6. While Java 1.4 has been in the field for quiet few years and personified as a de-facto across wide range of applications and industry choice, Java 1.5 has made its advent to an extent that many Java applications across the globe are now migrating to 1.5. Reason being simple, Java is backward compatible and richer features of Java 1.5. While Java 1.4 has persisted to demonstrate reliability, Java 1.5 has proved to be more plenteous. Relatively recent arrival of Java 1.6 has its share of the buzz with more features in the kit. Now, we have a sneak peak into Java 1.7 available as well. With every new release, new features in Java will be explored. As this post’s focus is on the installation/configuration facet, we shall keep the discussion of java versions, features, pros & cons as an open topic.

Many times, there’s confusion about PATH / CLASSPATH/ JAVA_HOME variables. What they actually are and how they matter? Or if its really necessary to set them, if so how to set them? Below we try to answer all the questions that matter.

The following sections describe:-

  • Downloading Instructions – Describes where and what to to download.
  • Installing Instructions – Describes how to install Java into a location in the computer.
  • Configuration Instructions – Describes how to set up a computer to write java programs and also execute them.

 

In brief:

  • Download Java (JDK – if you want to write and run your own java programs / JRE – if you only want to run java programs) from Sun’s website. (Chose your java version)
  • Once downloaded, install Java to any location on your computer
  • Set environment variables (PATH / CLASSPATH / JAVA_HOME – all optional and set for convinience) in your computer.
  • Set PATH to (java installed location)/JDK_verstion/bin (optional)
  • Set CLASSPATH to (java installed location)/JDK_verstion/lib/tools.jar (optional)
  • Set JAVA_HOME to (java installed location)/JDK_verstion (optional)

If you are using any IDE for working on java, you dont even have to set the environment variables, as the IDE itself ships with a support for a Java version. You have to set the environment variables most likely in situations like:

  • You want to work with simple text editors like notepad
  • You want to work with certain java dependant softwares like Ant, Glassfish, Tomcat etc which need java environment variables to be set.

Refer below detailed description for more information.

 

 

Downloading Instructions: Read more…