Install Sun JDK

1. Search for Sun JDK in package manager, and then install it.

2. Try running the command

sudo update-alternatives --config java

and choose a default java of your liking.

3. Set Sun's JVM as default Java version:

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

4. Edit /etc/jvm and move /usr/lib/jvm/java-1.5.0-sun to the top of JVMs offered:

sudo gedit /etc/jvm

5. Configure the Eclipse.
There is a bug right now were Eclipse ignores Ubuntu's java-common settings and uses its own (bug 45347). To work around the bug, you need to edit Eclipse's java_home file:

sudo -b gedit /etc/eclipse/java_home

and add

/usr/lib/jvm/java-1.5.0-sun

to the top of the file.

If this still not work, just add the new JRE at Eclipse Global Settings.