I currently have both Java 5 and Java 6 installed on my machine and it’s very easy to switch between the two. Java 6 has some nice goodies such as JSR-223 and better jconsole that I like to use.

For Java 5:

sudo apt-get install sun-java5-jre sun-java5-jdk


For Java 6:

sudo apt-get install sun-java6-jre sun-java6-jdk


There are other packages that you might be interested in:

• sun-java6-demo
• sun-java6-doc
• sun-java6-source

Verify that you have the correct version of java running:

java -version

To see a list of the java versions that you have installed, you can use the following command (it’s a letter L at the end of the command):

update-java-alternatives -l

This should show you a list of all the java alternatives you have installed. java-gcj is the free version of Java from the GNU project and comes installed by default with Ubuntu so you should see it. To switch to a different version, use the following command:

sudo update-java-alternatives -s <version-desired>

e.g:

sudo update-java-alternatives -s java-1.5.0-sun