There are two methods to install eclipse
1: By downloading form website and extracting and operating without involving registries.
2: From the Terminal by entering
sudo apt-get install eclipse
If you have installed it using the first method then you have to manually remove the directory where you installed Eclipse. Which Include the Eclipse workspace and Eclipse Directory.
And if you have installed it using the Terminal method.
Then the best method will be to first install synaptic package manager by typing
sudo apt-get install synaptic afterward opening synaptic search Eclipse and the Packages will appear. The one with the green box are installed right click on them and select complete removal. Do this for all remaining packages and apply. It will completely remove the eclipse form the system.