Java Reference
In-Depth Information
The
class
Math
contains a very useful method,
pow
, called the method
power
, which
is used to calculate
x
y
in a program, that is,
Math.pow(x, y) = x
y
. For example,
Math.pow(2,3) = 2
3
= 8
and
Math.pow(4, 0.5) = 4
0.5
=
p
4
= 2
. The numbers
x
and
y
used in the method
pow
are called the (actual) parameters of the method
pow
. For
example, in
Math.pow(2, 3)
, the parameters are
2
and
3
.
An expression such as
Math.pow(2, 3)
is called a method call, and causes the code
attached to the method
pow
to execute and, in this case, computes
2
3
. The method
pow
computes a value of type
double
. Therefore, we say that the return type of the method
pow
is
double
or the method
pow
is of type
double
.
In general, to use a predefined method in a program:
1. You need to know the name of the
class
containing the method.
2. You need to know the name of the
package
containing the
class
and
import this
class
from the
package
in the program.
3. You need to know the name of the method as well as the number of
parameters the method takes, the type of each parameter, and the order
of the parameters. You must also be aware of the return type of the
method or, loosely speaking, what the method produces.
For example, to use the method
nextInt
, you import the
class
Scanner
from the
package
java.util
.
3
As noted in Chapter 2, the Java system automatically imports methods and
class
es
from the
package
java.lang
. Therefore, you do not need to import any contents of
the
package
java.lang
explicitly. Because the
class
Math
is contained in the
package
java.lang
, to use the method
pow
, you need to know that the name of the
method is
pow
, that the method
pow
has two parameters, both of which are numbers, and
that the method calculates the first parameter to the power of the second parameter.
The program in the following example illustrates how to use predefined methods in a
program. More specifically, we use some math methods. Later in this chapter, after
introducing the
class
String
, we will show how to use
String
methods in a program.
EXAMPLE 3-1
public class
PredefinedMethods
{
public static void
main(String[] args)
{
double
u, v;
System.out.println("Line 1: 2 to the power "
+ "of 6 = " + Math.pow(2, 6));
//Line 1
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