Why is an ArrayList of ArrayLists not multidimensional?
arraylist, arrays, java, list, multidimensional-array
Solution
Cay S. Horstmann has stated within his book Core Java for the impatient:
There are no two-dimensional array lists in Java, but you can declare a variable of type `ArrayList<ArrayList<Integer>>` and build up the rows yourself.
due to the fact that `ArrayList`s can expand and shrink and become jagged rather than multi-dimensional, one could say it is not a two-dimensional array, multi-dimensional meaning fixed rows and columns, hence why I have also stated within the comments Java doesn't have true multi-dimensional arrays but this is outside the scope of your question.
if you're curious as to why I said Java doesn't have true multi-dimensional arrays have a read at the differences between a multidimensional array and an array of arrays in C#?
Just to make my answer clearer regarding whether Java has true multi-dimensional arrays or not, I did not say java doesn't have multi-dimensional arrays, I said Java doesn't have true multi-dimensional arrays and as expect the JLS has stated:
A multidimensional array need not have arrays of the same length at each level.
Problem
I recently appeared for an interview in which the interviewer asked me a question regarding `Arrays` and `ArrayList`. He asked me if an array of arrays can be multidimensional, then why is an `ArrayList` of `ArrayList`'s not multidimensional? For example: ``` // Multidimensional int[][] array = new int[m][n]; // Not multidimensional ArrayList<ArrayList<Integer>> seq = new ArrayList<ArrayList<Integer>>(); ``` Can anyone help me to understand this?