Using the Dynamic Java Component to create empty data records ?

I'm looking for some nice worked examples/documetnation of using the Dynamic Java Component to generate/insert new data records in the data stream. Or any advice on the best way to append new records into a preexisting record stream

eg

I have 100 records and I want to insert a new record in at postion 51 ,so I would end up with 101 records.

Many Thanks,

Paul.