How to fill a two Dimensional ArrayList in java with Integers?

Question

I have to create a 2d array with unknown size. So I have decided to go with a 2d ArrayList the problem is I\'m not sure how to initialize such an array or store information.

Answer 1

If you don't have all of the data in advance to be able to leverage aioobe's solution, you could use a Table from Google's Guava library.

Table matrix = new HashBasedTable();
matrix.put(rowIndex,columnIndex,value);

The primary drawback of this is that it's not incredibly fast or memory efficient if you are working with a large quantity of data, as everything is a hash lookup and primitives are wrapped by Integer.