http://java.sun.com/javase/downloads/index.jsp
or get an open source JDK, such as OpenJDK :
http://openjdk.java.net/
Under linux Ubuntu, you can for example get openjdk-6:
Important note:
Depending on your operating system, you may encounter problems with some open
source JRE/JDK. Please refer to section A.1.
You may need to adjust your JAVA_HOME environment variable, for example:
Under Windows, you may have to set the PATH environment variable to the JDK binaries.
Please check that you DO NOT USE a JDK from the GJC. To check, run on command line:
If your system is configured to use GJC, please download and install another JDK, and use it as default.
You may encounter problems using OpenJDK with Fedora distribution: Java does not
execute, or ViSiDiA graphical interface is altered (buttons are misalignmed for example).
In this case, please install and use the official Sun JRE/JDK.
Here is the recipe to install Sun JDK on Fedora (example is given for JDK 6 Update 16):