Hi Nelson
Unfortunately, UDF does not work with whole segments/structures - it requires individual fields of the source structure as input parameters.
Even if it does, unfortunately also, AFAIK there is no equivalent to the HR ABAP style of syntax in Java - there is no DO VARYING equivalent. Java works primarily with single primitive data types or object references.
You might have to built that gigantic 25 input UDF 
Rgds
Eng Swee