Different Numbers of Cells per Row

Each row of a 2D array may have a different number of cells. In the following example, the array uneven has

• 3 cells in its first row,
• 2 in its second row,
• and 5 in its last row.

An array element has to exist to be used in a program. If a program refers to an element that does not exist, bounds checking will catch the error (as the program runs) and generate an exception (which will usually halt your program.)

class UnevenExample
{
  public static void main( String[] arg )
  {
    // declare and construct a 2D array
    int[][] uneven = 
        { { 1, 9, 4 },
          { 0, 2},
          { 0, 1, 2, 3, 4 } };

    System.out.println("uneven[0][2] is ", + uneven[0][2] ) ; // OK 
    System.out.println("uneven[1][1] is ", + uneven[1][1] ) ; // OK 
    System.out.println("uneven[1][2] is ", + uneven[1][2] ) ; // WRONG! 

    uneven[2][4] = 97;  // OK 
    uneven[1][4] = 97;  // WRONG! 

    int val = uneven[0][2] ;  // OK 
    int sum = uneven[1][2] ;  // WRONG! 
  }
}

Making an assignment to an element that does not exist is an error. It will not create room in the array for the element.