Java Reference
In-Depth Information
1
// Fig. 10.11: Payable.java
2
// Payable interface declaration.
3
4
5
6
7
public
interface
Payable
{
double
getPaymentAmount();
// calculate payment; no implementation
}
Fig. 10.11
|
Payable
interface declaration.
We now create class
Invoice
(Fig. 10.12) to represent a simple invoice that contains bill-
ing information for only one kind of part. The class declares
private
instance variables
partNumber
,
partDescription
,
quantity
and
pricePerItem
(in lines 6-9) that indicate
the part number, a description of the part, the quantity of the part ordered and the price
per item. Class
Invoice
also contains a constructor (lines 12-26),
get
and
set
methods
(lines 29-69) that manipulate the class's instance variables and a
toString
method (lines
72-78) that returns a
String
representation of an
Invoice
object. Methods
setQuantity
(lines 41-47) and
setPricePerItem
(lines 56-63) ensure that
quantity
and
pricePer-
Item
obtain only nonnegative values.
1
// Fig. 10.12: Invoice.java
2
// Invoice class that implements Payable.
3
4
5
public
class
Invoice
implements
Payable
{
6
private final
String partNumber;
7
private final
String partDescription;
8
private
int
quantity;
9
private
double
pricePerItem;
10
11
// constructor
12
public
Invoice(String partNumber, String partDescription,
int
quantity,
13
double
pricePerItem)
14
{
15
if
(quantity <
0
)
// validate quantity
16
throw new
IllegalArgumentException(
"Quantity must be >= 0")
;
17
18
if
(pricePerItem <
0.0
)
// validate pricePerItem
19
throw new
IllegalArgumentException(
20
"Price per item must be >= 0"
);
21
22
this
.quantity = quantity;
23
this
.partNumber = partNumber;
24
this
.partDescription = partDescription;
25
this
.pricePerItem = pricePerItem;
26
}
// end constructor
27
Fig. 10.12
|
Invoice
class that implements
Payable
. (Part 1 of 3.)
