First of all, thanks a lot for your help. Now the code result that worked.

package com.eteks.test;

import java.net.URL;
import java.net.MalformedURLException;
import com.eteks.sweethome3d.plugin.Plugin;
import com.eteks.sweethome3d.plugin.PluginAction;
import com.eteks.sweethome3d.model ...

OK. Finally I've decided to learn more about java. Now I can set a predefined Jpg as backgroundimage from the menu bar.
My new question is: How could I autoload this plugin function when the application starts without clicking on the menu item?
Thanks in advance.

Hello all.
I would like to know if there is any way of execute a command to set the background image. Or command line.
I normally work with c# and before starting learning java, wanted to know if its possible to connect some simple functions like preferences,background image with c#.
Or if its ...