// Using length instead of hard-coded constants
static final int NUM_ROWS = 3;
static final int NUM_COLS = 5;
int[][] mat = new int [NUM_ROWS][NUM_COLS];
for ( int i=0; i<mat.length; i++ )
   {
   for ( int j=0; j<mat[i].length; j++ )
      {
      mat[i][j] = i*j+100;
      }
   }