I have a data structure like a database Rowset, which has got Rows and Rows have Columns. I need to initialize a Columns with null values, current code is to loop thru each column for a row and initialize values to NULL. Which is very inefficient if you have 100s or rows and 10s of column.

So instead I am keeping a initialized ArrayList of columns are RowSet level, and then doing a clone of this Arraylist for individual rows, as I believe clone() is faster than looping thru each element.

row.columnsValues = rowsset.NullArrayList.clone()

Problem with this is NullArrayList can be accidentally modified after being cloned, thus sacrificing the integrity of ArrayList at RowSet level, to prevent I am doing 3 things

1) Delcaring ArrayList as final 2) Any elements I insert are final or null 3) Methods thurough this arrayList are passed to other arrays are declared a final.

Sounds like a plan, do you see any holes ?