Java Reference
In-Depth Information
A program can create several arrays in a single declaration. The following declaration
reserves 100 elements for
b
and 27 elements for
x
:
String[] b =
new
String[
100
], x =
new
String[
27
];
When the type of the array and the square brackets are combined at the beginning of the
declaration, all the identifiers in the declaration are array variables. In this case, variables
b
and
x
refer to
String
arrays. For readability, we prefer to declare only
one
variable per dec-
laration. The preceding declaration is equivalent to:
String[] b =
new
String[
100
];
// create array b
String[] x =
new
String[
27
];
// create array x
Good Programming Practice 7.1
For readability, declare only one variable per declaration. Keep each declaration on a sep-
arate line, and include a comment describing the variable being declared.
When only one variable is declared in each declaration, the square brackets can be
placed either after the type or after the array variable name, as in:
String b[] =
new
String[
100
];
// create array b
String x[] =
new
String[
27
];
// create array x
but placing the square brackets after the type is preferred.
Common Programming Error 7.3
Declaring multiple array variables in a single declaration can lead to subtle errors. Consider
the declaration
int[] a, b, c;
. If
a
,
b
and
c
should be declared as array variables, then this
declaration is correct—placing square brackets directly following the type indicates that
all
the identifiers in the declaration are array variables. However, if only
a
is intended to be an
array variable, and
b
and
c
are intended to be individual
int
variables, then this declara-
tion is incorrect—the declaration
int a[], b, c;
would achieve the desired result.
A program can declare arrays of any type. Every element of a primitive-type array con-
tains a value of the array's declared element type. Similarly, in an array of a reference type,
every element is a reference to an object of the array's declared element type. For example,
every element of an
int
array is an
int
value, and every element of a
String
array is a ref-
erence to a
String
object.
This section presents several examples that demonstrate declaring arrays, creating arrays,
initializing arrays and manipulating array elements.
The application of Fig. 7.2 uses keyword
new
to create an array of 10
int
elements, which
are initially zero (the default initial value for
int
variables). Line 9 declares
array
—a ref-
erence capable of referring to an array of
int
elements—then initializes the variable with
a reference to an array object containing 10
int
elements. Line 11 outputs the column
headings. The first column contains the index (0-9) of each array element, and the second
column contains the default initial value (0) of each array element.
