How to Change the Resolution of a Java Game/Application
With this you can change the resolution of Java games so that they run fullscreen instead of in a smaller window.Make sure you have WinRAR. open up the.jar game with it by right-clicking on the file, open with WinRAR. go to “META-INF” folder and extract the “manifest.mf” file in der to wherever. open the extracted file by right-clicking on it, open with Notepad. check the “always use this program” box.
Edit file “manifest.mf” Than write there this in the end:

Nokia-MIDlet-Original-Display-Size: 176 ,208
Nokia-MIDlet-Target-Display-Size: 352 ,416

MIDlet-Original-Display-Size: 128 ,160
Nokia-MIDlet-Target-Display-Size: 240 ,320

Change the values for your phone and app. ‘Original’ size is the native resolution of the game, and ‘target’ size is the resolution of your phone. Change these numbers as appropriate… when ur done, drag it back into the “META-INF” folder. overwrite the previous file. Hope this helps.

[Via NokiaSymbianBlog]