I'm publishing the source code for a platform jumper i need help with the ground detection and the jumping and falling any other tips would be nice. The scenario is called Treasure Hunt.
Maybe my Operation: Crashtest game can help you. If you have a look at the world classe getMaterialAt or getMaterialNumberAt that may help you with the ground detection.
For jumping and falling you should have a look in the Hero class. Especally the methods for movement and the setLocation methods.