Q:

Cannot add an application to the launcher

I've downloaded Eclipse and I want it to be on my fast-launching dash bar but the problem is that, as you all probably know, Eclipse does not install but is inside a normal archive.
So I tried to make my own .desktop file and placed it in ~/.local/share/applications but it didn't change anything.
So I downloaded alacarte and tried to add a menu element but every time I hit the "OK" button nothing happened (there wasn't anything new on the alacarte list, of course nor on the dash bar).
So what should I do and why nothing I've been doing seemed to work?
Mine .desktop file:

[Desktop Entry]
Name=Eclipse\ Java
Comment=Eclipse\ Luna\ do\ pracy\ przy\ Javie
Exec=./~/home/jantek/Instalki/Eclipse\ Java/eclipse/eclipse
Icon=./~/home/jantek/Instalki/Eclipse\ Java/eclipse/icon.xpm
Terminal=false
Type=Application
StartupNotify=true
 And the alacartes one:

[Desktop Entry]
Comment=Eclipse Luna dla Javy
Terminal=false
Name=Eclipse Java
Exec=/home/jantek/Instalki/Eclipse Java/eclipse/eclipse
Type=Application
Icon=/home/jantek/Instalki/Eclipse Java/eclipse/icon

A:

Issues with the desktop file
Taking the alacarte-made desktop file as a starting point (the other one has more issues), there are two lines which are almost certainly critical, and causing your desktop file to be refused by Dash and the Launcher:

The Exec= line:
Exec=/home/jantek/Instalki/Eclipse Java/eclipse/eclipse

What you are actually trying to do here is to open a file Java/eclipse/eclipse with an executable called Eclipse, located in /home/jantek/Instalki:
Exec=<application> <file>

That is probably not what you intended. Instead of the application (eclipse), you are referring to what seems to be a directory (Exec=/home/jantek/Instalki/Eclipse). 
Assuming the executable eclipse (lowercase) is in the folder .../Eclipse (looking at your Icon= line, but check it), your Exec= line simply should be like:
Exec=/home/jantek/Instalki/Eclipse/eclipse

The Icon= line:
Like I mentioned in my comment, Alacarte removes the file extension of any icon you define. Apart from that, just like in the Exec= line, the path you are defining is incorrect (why the space?). Your Icon= line should look like:
Icon=/home/jantek/Instalki/Eclipse/icon.xpm

But again, check if the paths to both the eclipse executable and the icon are correct.

If you fix these two lines, your .desktop file should work fine.
Note:
If the path to your executable or your icon includes foldernames with spaces:

If it is in the Exec= line, put either the whole part after Exec= in quotes:
Exec="/long/path/to/executable/folder with spaces/eclipse"

or just the folder with spaces:
Exec=/long/path/to/executable/"folder with spaces"/eclipse

In the Icon= line, a folder with a space should be fine:
Icon=/long/path/to/executable/folder with spaces/icon.xpm

