Java: How to store a 2D array within a 1D array -

i trying store found 2d array 1d array faster processing later. however, keep getting nullpointerexception when try fill 1d array. happens txt file has number of rows , colums read first row , column amount doing 2d array. each index reads next data element on txt file , stores @ index until 50 000 integer values stored. works fine.

now want take 2d array , store elements 1d array faster processing later when looking answers without using array list or put them in order, fine,

int [][] data = null;  int[] arraycount = null;  (int row = 0; row < numberofrows; row++) {     (int col = 0; col < numberofcols; col++)       {         data[row][col] = inputfile.nextint();     } }  //doesn't work gives me excpetion data[0][0] = arraycount[0]; 

i tried in loops no matter nullpointerexception

you haven't initialized data , arraycount variables, initialize follows :

int[][] data = new int[numberofrows][numberofcols]; int[] arraycount = new int[numberofrows * numberofcols]; 

in case, copy 2d 1d array may use :

    numberofrows = data.length;     if (numberofrows > 0) {         numberofcols = data[0].length;     } else {         numberofcols = 0;     }      system.out.println("numberofrows : "+numberofrows);     system.out.println("numberofcols : "+numberofcols);      (int row = 0, count = 0; row < numberofrows; row++) {         (int col = 0; col < numberofcols; col++) {             arraycount[count] = data[row][col];             count++;         }     }