ARRAYS - Java Programming: From Problem Analysis to Program Design - page 596

matrix

[0] [1] [2] [3] [4] [5]

[0]

[1]

[2]

[3]

[4]

[5]
[6]

FIGURE 9-21 Two-dimensional array matrix

For the two-dimensional array matrix , the value of matrix.length is 7 , which
is the same as the value of the named constant ROWS . Also, the values of
matrix[0].length , matrix[1].length ,..., matrix[6].length give
the number of columns in row 0, row 1, . . ., row 6, respectively. Notice that the
number of columns in each row is 6.

Because all the elements of a two-dimensional array are of the same type, the elements of
any row or column are of the same type. This means that in a two-dimensional array, the
elements of each row and each column can be processed as a one-dimensional array.
Therefore, when processing a particular row or column of a two-dimensional array, we use
algorithms similar to those that process one-dimensional arrays. We explain this concept
further with the help of the two-dimensional array matrix , as declared previously.
Suppose that we want to process row number 5 of matrix (the sixth row of matrix ).
The elements of row number 5 of matrix are:
matrix[5][0], matrix[5][1], matrix[5][2], matrix[5][3], matrix[5][4],
matrix[5][5]
In these elements, the first index (the row position) is fixed at 5 . The second index (the
column position) ranges from 0 to 5 . Therefore, we can use the following for loop to
process row number 5 :

for ( int col = 0; col < matrix[5].length; col++)
//process matrix[5][col]
This for loop is equivalent to the following for loop:

int row = 5;

for ( int col = 0; col < matrix[row].length; col++)
//process matrix[row][col]