Java Reference
In-Depth Information
indexed
variables
The
indexed variables
for this array each have two indices. For example,
page[0]
[0]
,
page[15][32]
, and
page[29][99]
are three of the indexed variables for this
array. Note that each index must be enclosed in its own set of square brackets. As was
true of the one-dimensional arrays we have already seen, each indexed variable for a
multidimensional array is a variable of the base type—in this case, the type
char
.
An array may have any number of indices, but perhaps the most common number is
two. A two-dimensional array can be visualized as a two-dimensional display with the
first index giving the row and the second index giving the column. For example, the
array indexed variables of the two-dimensional array
a
, declared and created as
char
[][] a =
new char
[5][12];
can be visualized as follows:
a[0][0], a[0][1], a[0][2], ..., a[0][11]
a[1][0], a[1][1], a[1][2], ..., a[1][11]
a[2][0], a[2][1], a[2][2], ..., a[2][11]
a[3][0], a[3][1], a[3][2], ..., a[3][11]
a[4][0], a[4][1], a[4][2], ..., a[4][11]
You might use the array
a
to store all the characters on a (very small) page of text that has
5 lines (numbered 0 through 4) and 12 characters on each line (numbered 0 through 11).
Declaring and Creating a Multidimensional Array
You declare a multidimensional array variable and create a multidimensional array object in
basically the same way that you create and name a one-dimensional array. You simply use
as many square brackets as there are indices.
SYNTAX
Base_Type
[]...[]
Variable_Name
=
new
Base_Type
[
Length_l
]
…
[
Length_n
]
;
EXAMPLES
char
[][] a =
new char
[5][12];
char
[][] page =
new char
[30][100];
double
[][] table =
new double
[100][10];
int
[][][] figure =
new int
[10][20][30];
Person[][] entry =
new
Person[10][10];
Person
is a class.
a multi-
dimensional
array is an
array of
arrays
In Java, a two-dimensional array, such as
a
, is actually an array of arrays. The
above array
a
is actually a one-dimensional array of size
5
, whose base type is a one-
dimensional array of characters of size
12
. This is diagrammed in Display 6.17 . As
shown in that display, the array variable
a
contains a reference to a one-dimensional
array of length
5
with a base type of
char[]
; that is, the base type of
a
is the type for an
entire one-dimensional array of characters. Each indexed variable
a[0]
,
a[1]
, and so
forth contains a reference to a one-dimensional array of characters.
