Running Java under Ubuntu

Java

Sun Microsystems have developed Java, which is many things depending on who you ask. It is a language, and an execution environment and probably many more things. On this page Java refers to the software that executes programs compiled to Java byte codes (akin to machine language).

Installation

In order to run Java programs and Java applets, you must have a Java environment installed. The GCJ flavor of Java is installed as default, and is usually fine for most purposes. You may, however, have a need to run the Sun flavor of Java if something does not work correctly.

To get Sun Java under Ubuntu 7.04 or later running on Intel or PowerPC platform, you should enable the Universe repository in Add/Remove programs, and install either the openjdk-6-jre package or the sun-java6-bin package. (Note: PowerPC version is slow).

To get Sun Java under Ubuntu 6.06 or 6.10 running on Intel x86 platform, you should enable the Universe repository in Add/Remove programs, and install the sun-java5-bin package.

Note: The same commands will work under Xubuntu/Kubuntu (using Add/Remove or the Adept Package Installer).

See JavaInstallation for details about installation of other flavors of Java.

Choosing the default Java to use

Just installing new Java flavours does not change the default Java pointed to by /usr/bin/java. You must explicitly set this:

  • Open a Terminal window
  • Run sudo update-java-alternatives -l to see the current configuration and possibilities.
  • Run sudo update-java-alternatives -s XXXX to set the XXX java version as default. For Sun Java 6 this would be sudo update-java-alternatives -s java-6-sun
  • Run java -version to ensure that the correct version is being called.

You can also use the following command to interactively make the change;

  • Open a Terminal window
  • Run sudo update-alternatives --config java
  • Follow the onscreen prompt

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