Java Reference
In-Depth Information
With this observation, you can easily identify all the cells in the box. For instance, if
grid[r][c]
is the starting cell of a
3
*
3
box, the cells in the box can be traversed in a
nested loop as follows:
// Get all cells in a 3-by-3 box starting at grid[r][c]
for
(
int
row = r; row < r +
3
; row++)
for
(
int
col = c; col < c +
3
; col++)
// grid[row][col] is in the box
It is cumbersome to enter 81 numbers from the console. When you test the program, you may
store the input in a file, say
CheckSudokuSolution.txt
(see
www.cs.armstrong.edu/liang/data/
CheckSudokuSolution.txt
), and run the program using the following command:
java CheckSudokuSolution < CheckSudokuSolution.txt
input file
A two-dimensional array consists of an array of one-dimensional arrays and a three-
dimensional array consists of an array of two-dimensional arrays.
Key
Point
In the preceding section, you used a two-dimensional array to represent a matrix or a table.
Occasionally, you will need to represent
n
-dimensional data structures. In Java, you can cre-
ate
n
-dimensional arrays for any integer
n
.
The way to declare two-dimensional array variables and create two-dimensional arrays can
be generalized to declare
n
-dimensional array variables and create
n
-dimensional arrays for
For example, you may use a three-dimensional array to store exam scores for a class
of six students with five exams, and each exam has two parts (multiple-choice and essay). The
following syntax declares a three-dimensional array variable
scores
, creates an array, and
assigns its reference to
scores
.
n
7=
3.
double
[][][] scores =
new double
[
6
][
5
][
2
];
You can also use the short-hand notation to create and initialize the array as follows:
double
[][][] scores = {
{{
7.5
,
20.5
}, {
9.0
,
22.5
}, {
15
,
33.5
}, {
13
,
21.5
}, {
15
,
2.5
}},
{{
4.5
,
21.5
}, {
9.0
,
22.5
}, {
15
,
34.5
}, {
12
,
20.5
}, {
14
,
9.5
}},
{{
6.5
,
30.5
}, {
9.4
,
10.5
}, {
11
,
33.5
}, {
11
,
23.5
}, {
10
,
2.5
}},
{{
6.5
,
23.5
}, {
9.4
,
32.5
}, {
13
,
34.5
}, {
11
,
20.5
}, {
16
,
7.5
}},
{{
8.5
,
26.5
}, {
9.4
,
52.5
}, {
13
,
36.5
}, {
13
,
24.5
}, {
16
,
2.5
}},
{{
9.5
,
20.5
}, {
9.4
,
42.5
}, {
13
,
31.5
}, {
12
,
20.5
}, {
16
,
6.5
}}};
scores[0][1][0]
refers to the multiple-choice score for the first student's second exam,
which is
9.0
.
scores[0][1][1]
refers to the essay score for the first student's second
exam, which is
22.5
. This is depicted in the following figure:
Which student
Which exam
Multiple-choice or essay
scores [i] [j] [k]
A multidimensional array is actually an array in which each element is another array. A three-
dimensional array consists of an array of two-dimensional arrays. A two-dimensional array
consists of an array of one-dimensional arrays. For example, suppose
x = new
int[2][2][5]
, and
x[0]
and
x[1]
are two-dimensional arrays.
X[0][0]
,
x[0][1]
,
x[1][0]
, and
x[1][1]
are one-dimensional arrays and each contains five elements.
