Java Reference
In-Depth Information
2.2
The black-box view of a method
You know that a
method
is the programming equivalent of a recipe. We now see
how methods are used in Java.
Activity
2-1.2
2.2.1
The anatomy of a method header
The definition of a method has three parts: specification, header, and body. Here,
we describe the first two parts, which are used to understand a call on a method.
When you call a method, we say that you are the
client
or
customer
of the
method. Below is a method definition, with the contents of the body not shown:
/**
Draw a line in graphics window from
pixel
(x1, y1)
to
(x2, y2) */
public void
drawLine(
int
x1,
int
y1,
int
x2,
int
y2) {
…
}
The first part of a method declaration is a comment that describes what the
method does. It is called a
specification
. As you can see from the specification
given above, method
drawLine
draws a line in the graphics window.
The second part of a method declaration is the
method header
, which con-
tains (in order) these items:
Style Note
13.1.2:
method names
•
Modifiers
. In this header, the one modifier,
public
, indicates that every
class can use this method. (You will see
private
methods later on.)
•
The return type
. Keyword
void
indicates that this method is a
proce-
dure
, which is a method that does not return a value. For a
function
, the
type of value the function returns replaces
void
.
•
The name of the method
, in this case,
drawLine
.
•
Declarations of the parameters
of the method, enclosed in parentheses
and separated by commas. Each parameter declaration consists of a type
and the name of the parameter (which is an identifier). In this case, all
four parameters —
x1
,
y1
,
x2
, and
y2
— are of type
int
.
The
signature
of a method consists of the name of the method and the num-
ber and types of is parameters. We write the signature of
drawLine
as follows:
drawLine(
int
,
int
,
int
,
int
)
The idea of a parameter was discussed in Sec. 2.1 when relating methods to
recipes. There, a parameter
X
was associated with a value —a bunch of prunes or
apricots. Similarly, in Java, a value gets associated with the parameter when the
method is called. The idea of a parameter may still seem foreign to you, so we
recommend that you memorize the following definition:
Style Note
13.1.1:
parameter
names
Parameter
: A parameter is a variable that is declared within the
parentheses of a method header.
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