Java Reference
In-Depth Information
which is equivalent to
x =
1
;
System.out.println(x);
If a value is assigned to multiple variables, you can use this syntax:
i = j = k =
1
;
which is equivalent to
k =
1
;
j = k;
i = j;
Note
In an assignment statement, the data type of the variable on the left must be compatible
with the data type of the value on the right. For example,
int x = 1.0
would be illegal,
because the data type of
x
is
int
. You cannot assign a
double
value (
1.0
) to an
int
variable without using type casting. Type casting is introduced in Section 2.15.
A named constant is an identifier that represents a permanent value.
Key
Point
The value of a variable may change during the execution of a program, but a
named constant,
or simply
constant,
represents permanent data that never changes. In our
ComputeArea
pro-
gram, is a constant. If you use it frequently, you don't want to keep typing
3.14159
;
instead, you can declare a constant for
constant
p
p
.
Here is the syntax for declaring a constant:
final
datatype CONSTANTNAME = value;
A constant must be declared and initialized in the same statement. The word
final
is a
Java keyword for declaring a constant. For example, you can declare
final keyword
p
as a constant and
rewrite Listing 2.1 as follows:
// ComputeArea.java: Compute the area of a circle
public class
ComputeArea {
public static void
main(String[] args) {
// Declare a constant
final double
PI =
3.14159
;
// Assign a radius
double
radius =
20
;
// Compute area
double
area = radius * radius * ;
PI
// Display results
System.out.println(
"The area for the circle of radius "
+
radius +
" is "
+ area);
}
}
There are three benefits of using constants: (1) You don't have to repeatedly type the same
value if it is used multiple times; (2) if you have to change the constant value (e.g., from
3.14
to
3.14159
for
PI
), you need to change it only in a single location in the source code;
and (3) a descriptive name for a constant makes the program easy to read.
benefits of constants