Java Runtime Environment (JRE)

The Java Runtime Environment (JRE) is needed to run Java applications.

The JRE does not contain development tools. You need the Java Development Kit (JDK) or a comparable solution to develop Java applications.

Terms

JRE

Java Runtime Environment. Needed to run Java applications on your platform. There are Open Source JREs and the “original” JRE by Oracle (former Sun Microsystems).

JVM

Java Virtual Machine. Part of the JRE, executes the Java code you want to run.

JDK

Java Development Kit (JDK). A development tool needed by programmers to compile Java programs. The JDK brings the complete JRE – if you want to install the JDK, there is no need to install the JRE separately. There are Open Source JDKs and the “original” JDK by Oracle (former Sun Microsystems).

Java SDK

Java Software Development Kit, a synonym for the JDK.

Installation

Ubuntu

10.04 Lucid and above

You can choose between two1) Open Source JREs and the “original” JRE by Oracle (former Sun Microsystems).

If you don't know which JRE to choose, take the one by Oracle/Sun to be on the safe side – some rare applications simply do not work without the proprietary one. Additionally, some users may have to run applications which are certified for the Oracle JRE only, loosing support if they use another JRE.

Oracle Java (former Sun Java)

If not already done, you have to add the partner repository first.

Simply install the following package(s):

There are some additional packages, providing special functionality:

  • sun-java6-plugin (partner) – Java plugin for your webbrowser. Needed to run Java Applets on websites.
OpenJDK

Simply install the following package(s):

Windows

XP and above

The only really usable JRE on Windows systems is the proprietary JRE by Oracle (sometimes called “Java SE Runtime Environment”). Simply download the Windows installer and execute it with administrator privileges.

Watch out for the Yahoo! and/or Google Browser Toolbar or other software you may not want. The Java installer tries to install such 3rd party components by default. This is also important for Java Updates. (data as per 2010-07-06)

Tips and tricks

Choosing the default JRE (Ubuntu Linux)

Even it is not recommended to install more than one JRE, it is possible to have e.g. the OpenJDK JRE and Oracle Java JRE installed at the same time on the same machine. To choose the default one called by java on your command line, run the following:

sudo update-alternatives --config java
1) OpenJDK and GNU Java. I do not cover GNU Java on this page because OpenJDK's JRE simply works better in my experience.
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