Recs.
Updated
SpecsUpdate
Pros
Pro Java is a great development platform
Java is a well-optimized just-in-time compiled language. It's faster than languages without an effective native-code compiler such as Python or Ruby, similar in speed to other just-in-time compiled languages such as C#, while slightly slower than compiled languages such as C or C++ (with some low-level and numeric benchmarks being similar to C++).
Java also has a wide variety of high-class IDEs available.
Pro Free and open-source
jMonkey is completely free, meaning it's possible to develop and release a game with no fees or royalties. Because it is open-source, jMonkey has plenty of people fixing bugs and, adding to the engine as well as creating a variety of plugins that can be used in the engine.
Cons
Con Very limited
JME is more of a collection of libraries patched together than a cohesive engine. To use it effectively you need to use a separate frontend like NetBeans using jMonkey plugins. If you go the normal route your development time will be much longer. And at the end of all that it doesn't even support that many platforms and runs on Java meaning less performance (3D).