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tor of the superclass that has one parameter, of class int . SR8. private . SR9.
Yes, it can make sense. In implementing a class based on its specification, it may
be advantageous or necessary to add new methods for simplicity or readability
(or other reasons). These new methods are not mentioned in the specification and
should not be available to users of the class. SR10. Class Object . SR11.
equals(Object) and toString() . SR12. It should be an equivalence relation:
reflexive, symmetric, and transitive. SR13. If a B is a C, then B should be a sub-
class of C. SR14. False. SR15. A class invariant is a relation concerning the
fields of the class that should be true before and after each method of the class is
called. Essentially, the class invariant is given by the group of definitions of the
fields of the class. SR16. When determining the instance method to call (within
a folder) for a call method-name ( arguments ) , start at the bottom of the folder
and search upward until the appropriate method is found.
Exercises for Chapter 4
E1. Obtain classes Employee , Executive , and HourlyEmployee that are dis-
cussed in Sec. 4.1 from a footnote on Lesson page 4-1 of the CD. Design and
implement a fourth class, SalariedEmployee . An instance of this class repre-
sents an employee that is paid on a yearly basis; the employee gets no bonus and
no overtime.
E2. Add a constructor to class Employee (and the other classes as well) of
Exercise E1 that initializes the hire date with the date at which an instance is cre-
ated. Thus, in Employee , this constructor has only one parameter, the name of the
E3. Design and implement a class Manager , which extends class Salaried-
Employee of Exercise E1. An instance should contain the name of the depart-
ment that the manager manages. You determine what extra methods are needed
and what function toString should produce.
E4. Design and implement a class Address , which contains a house number,
street name, city, state, and zip code (for a house in the United States). Add a
field to class Employee of Exercise E1 to contain the address of an employee,
and add whatever methods are needed to make it accessible from outside the
E5. Suppose you are going to implement a set of classes that, together, describe
modes of transportation (e.g. plane, auto). Each of these modes has its own sub-
modes (e.g. an auto could be a car, SUV, truck, etc. Develop a hierarchy of such
modes of transportation, which would end up being a hierarchy of classes and
subclasses. This is an open-ended question, and there is no single answer.
E6. Turn to lesson page 4-1 on the ProgramLive CD and click on “Proj”. A win-
dow opens, with some projects in it. Carry out project “Movie reviews”.
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