Java Reference
In-Depth Information
Display 8.6
Employee
Class and Its Derived Classes
(part 2 of 2)
1
public class HourlyEmployee extends
Employee
2 {
3
private double
wageRate;
4
private double
hours;
//for the month
5
/**
6
Returns the pay for the month
.
7
*/
8
public double
getPay()
9 {
10
return
wageRate * hours;
11 }
12
public boolean
equals(Object otherObject)
13 {
14
if
(otherObject ==
null
)
15
return false
;
16
else if
(getClass() != otherObject.getClass( ))
17
return false
;
18
else
19 {
20 HourlyEmployee otherHourlyEmployee =
21 (HourlyEmployee)otherObject;
22
return
(
super
.equals(otherHourlyEmployee)
23 && (wageRate == otherHourlyEmployee.wageRate)
24 && (hours == otherHourlyEmployee.hours));
25 }
26 }
All constructor and other method definitions are exactly the same as in Display 7.3.
27 }
If we add this abstract method
getPay
to the class
Employee
, then we are free to add
the method
samePay
to the class
Employee
.
An abstract method can be thought of as the interface part of a method with the
implementation details omitted. Because a private method is normally only a helping
method and so not part of the interface for a programmer using the class, it follows that
it does not make sense to have a private abstract method. Java enforces this reasoning.
In Java, an abstract method cannot be private. Normally an abstract method is public
but protected, and package (default) access is allowed.
An abstract method serves a purpose, even though it is not given a full definition. It
serves as a placeholder for a method that must be defined in all (nonabstract) derived
classes. Note that in Display 8.7 , the method
samePay
includes invocations of the
method
getPay
. If the abstract method
getPay
were omitted, this invocation of
getPay
would be illegal.
abstract
cannot be
private
