hey,
i'd like to know if there is a java program that transformate 2D dicom images to 3D dicom images?

There may be but as I took a look at https://www.google.com/search?q=2D+dicom+images+to+3D+dicom+image&gl=US it appears this area is either proprietary or being researched.

As you are researching this I have to ask you to share your research results as well. I found no free or open source Java code to do what you asked but this area is being researched (see researchgate discussions.)

If you want to create such and open source it, you would be among the first.