.txt file to multidimensional array

I have a .txt file that contains either i's or j's. There are 7000 characters in total which are all either i or j. I need to place these into an array where each row is 70 characters long and there are a 100 rows in total. I have a custom package based on the buffered reader which can read in the values. I am pretty sure I need to use a loop to loop through all the character values but I am lost as to what loop to use and how to use it in the correct way. Any help would be greatly appreciated :) .

There are essentially two types of loop - counting loops when the set size is known, and conditional loops where looping is infinite until a condition is met. A for-loop is a great example of a counting loop, as it loops i times, where i is a number you predefine. A while-loop is the other kind and terminates based on a boolean condition.

Which type of loop do you think you need and why?