Hello,
I am not sure if your issue is resolved yet but perhaps this helps to get your problem more clear.
First something about an Array.. consider an Array to be sort of a list with an index or as I call it positions from 0 to your Array end.
Each position can contain an object or a variable or a null value which is stored in the memory for later use. (as long as the program is running ofc)
What likely could have happened is that your program tried to access a position which is OUTside the array, hence the "out of bound" exception.
Simple example.. you have an array length of 10 (positions from 0 - 9) you try to access position #10.. BOOM array out of bound.
Hope it helps.