How to increase or decrease size of a matrix in Java? -

i have m×n matrix , need change number of columns (increase or decrease). have following code not work.

public class resize {      public static int [][] = new int [2][2];     public static int i, j;      public static void main(string[] args) {         = (int[][])resizearray(a,4);         for(i = 0 ; < 2 ; i++){         for(j = 0 ; j < 4 ; j++){             a[i][j] = j+i;             system.out.print(a[i][j]+"   ");         }         system.out.println("");     } } // resize arr dimension n = 20 dimension n = 14  /////////////// private static object resizearray (object oldarray, int newsize) {        int oldsize = java.lang.reflect.array.getlength(oldarray);        class elementtype = oldarray.getclass().getcomponenttype();        object newarray = java.lang.reflect.array.newinstance(elementtype, newsize);        int preservelength = math.min(oldsize, newsize);        if (preservelength > 0)           system.arraycopy(oldarray, 0, newarray, 0, preservelength);        return newarray;      } } 

the problem you're changing number of rows rather number of columns in resizearray method. can tell printing @ end of main method, a.length, equals number of rows in 2d array. line

int oldsize = java.lang.reflect.array.getlength(oldarray); 

is same setting oldsize a.length. both agree oldsize number of rows in inputted array. , line

system.arraycopy(oldarray, 0, newarray, 0, preservelength); 

copies elements oldarray[0], oldarray[1], oldarray[2], ... oldarray[preservelength - 1] newarray[0], newarray[1], newarray[2], ... newarray[preservelength - 1] respectively. 2d array, you're copying rows of old array , putting them new array.

a possible solution make new array of size math.min(oldarray[0].length, newlength) , loop through new array putting elements old array new array.

private static int[][] resizearray (int[][] oldarray, int newsize) {    int oldsize = oldarray[0].length; //number of columns    int preservelength = math.min(oldsize, newsize);    int[][] newarray = new int[oldarray.length][newsize];    for(int = 0; < oldarray.length; i++) {        for(int j = 0; j < preservelength; j++) {            newarray[i][j] = oldarray[i][j];        }    }     return newarray;   }