From a desktop developer point of view, I will not write Java code.
There are two reasons for it:
1. I don't like or know Java.
2. I have a lot of C code and C libraries that I use.
If I were to port an application, I would much rather spend a few days making it compatible with a new platform (stuff like screen size, lack of mouse, etc.) than rewrite ALL my code in Java.

And of course, Java is slower than C/C++, which means that more powerful CPUs are needed, which will eat your battery more.

Oh, and one more thing: Most of the cellphones use ARM based CPUs, there is no need to use Java or .NET stuff.