Java Reference
In-Depth Information
boss
worker1
worker2
worker3
worker4
worker5
Fig. 6.1
|
Hierarchical boss-method/worker-method relationship.
Although most methods execute in response to method calls
on
specific objects
, this is not
always the case. Sometimes a method performs a task that does not depend on an object.
Such a method applies to the class in which it's declared as a whole and is known as a
stat-
ic
method or a
class method
.
It's common for classes to contain convenient
static
methods to perform common
tasks. For example, recall that we used
static
method
pow
of class
Math
to raise a value to
a power in Fig. 5.6. To declare a method as
static
, place the keyword
static
before the
return type in the method's declaration. For any class imported into your program, you
can call the class's
static
methods by specifying the name of the class in which the
method is declared, followed by a dot (
.
) and the method name, as in
ClassName
.
methodName
(
arguments
)
Math
Class Methods
We use various
Math
class methods here to present the concept of
static
methods. Class
Math
provides a collection of methods that enable you to perform common mathematical
calculations. For example, you can calculate the square root of
900.0
with the
static
method call
Math.sqrt(
900.0
)
This expression evaluates to
30.0
. Method
sqrt
takes an argument of type
double
and re-
turns a result of type
double
. To output the value of the preceding method call in the com-
mand window, you might write the statement
System.out.println(Math.sqrt(
900.0
));
In this statement, the value that
sqrt
returns becomes the argument to method
println
.
There was no need to create a
Math
object before calling method
sqrt
. Also
all
Math
class
methods are
static
—therefore, each is called by preceding its name with the class name
Math
and the dot (
.
) separator.
Software Engineering Observation 6.4
Class
Math
is part of the
java.lang
package, which is implicitly imported by the compiler,
so it's not necessary to import class
Math
to use its methods.
