A deformable terrain is something that can have a serious effect on the gameplay, or it can simply be a cosmetic bonus. It can be used for impact craters or games that require excavation.
We'll base the deformation around the Control class pattern as this allows us to offset the code in a manageable and reusable way. The recipe will trigger the deformation based on a mouse click, and it will use a ray to detect the collision point.
To get up and running quickly, unless there already is an application to apply this to, TestTerrain.java from the jMonkeyEngine's test cases will provide a good start for what we need. This example will expand on the code provided in that application, but it should work perfectly well with any terrain-based application.