Java Reference
In-Depth Information
objects. The program will iterate through the array and call method
earnings
for each
Employee
object. Java processes these method calls
polymorphically
. Declaring
earnings
as
an
abstract
method in
Employee
enables the calls to
earnings
through
Employee
variables
to compile and forces every direct
concrete
subclass of
Employee
to
override
earnings
.
Method
toString
in class
Employee
returns a
String
containing the first name, last
name and social security number of the employee. As we'll see, each subclass of
Employee
overrides
method
toString
to create a
String
representation of an object of that class that
contains the employee's type (e.g.,
"salaried employee:"
) followed by the rest of the
employee's information.
Let's consider class
Employee
's declaration (Fig. 10.4). The class includes a con-
structor that receives the first name, last name and social security number (lines 11-17);
get
methods that return the first name, last name and social security number (lines 20-23,
26-29 and 32-35, respectively); method
toString
(lines 38-43), which returns the
String
representation of an
Employee
; and
abstract
method
earnings
(line 46), which
will be implemented by each of the
concrete
subclasses. The
Employee
constructor does
not
validate its parameters in this example; normally, such validation should be provided.
1
// Fig. 10.4: Employee.java
2
// Employee abstract superclass.
3
4
public abstract class
Employee
5
{
6
private final
String firstName;
7
private final
String lastName;
8
private final
String socialSecurityNumber;
9
10
// constructor
11
public
Employee(String firstName, String lastName,
12
String socialSecurityNumber)
13
{
14
this.
firstName = firstName;
15
this.
lastName = lastName;
16
this.
socialSecurityNumber = socialSecurityNumber;
17
}
18
19
// return first name
20
public
String getFirstName()
21
{
22
return
firstName;
23
}
24
25
// return last name
26
public
String getLastName()
27
{
28
return
lastName;
29
}
30
31
// return social security number
32
public
String getSocialSecurityNumber()
33
{
Fig. 10.4
|
Employee
abstract superclass. (Part 1 of 2.)
