Chapter 4. Inheritance

Transcription

1 Chapter 4 Inheritance CSC 113 King Saud University College of Computer and Information Sciences Department of Computer Science Dr. S. HAMMAMI

2 Objectives In In this this chapter you you will will learn How How inheritance promotes software reusability. The The notions of of superes and and subes. To To use use keyword extends to to create a that that inherits attributes and and behaviors from from another. To To use use access modifier to to give give sub methods access to to super members. To To access super members with with super. How How constructors are are used used in in inheritance hierarchies. The The methods of of Object, the the direct or or indirect super of of all all es in in Java. Java.

3 OUTLINE Introduction Defining Classes with with Inheritance Inheritance and and Member Accessibility Inheritance Hierarchy Declaring Subes Inheritance and and Constructors Examples

4 1. Introduction Inheritance is is the the sharing of of attributes and and methods among es. We We take take a (super), and and then then define other es based on on the the first first one one (sub). The The sub inherit all all the the attributes and and methods of of the the super, but but also also have have attributes and and methods of of their own. own. Software reusability Create new new from existing Absorb existing s data data and and behaviors Enhance with with new new capabilities Sub extends super Sub More More specialized group group of of objects objects Behaviors inherited from from super Can Can customize Additional behaviors

5 Introduction Class Class hierarchy hierarchy Direct Direct super super Inherited Inherited explicitly explicitly (one (one level level up up hierarchy) hierarchy) Indirect Indirect super super Inherited Inherited two two or or more more levels levels up up hierarchy hierarchy Single Single inheritance inheritance Inherits Inherits from from one one super super Multiple Multiple inheritance inheritance Inherits Inherits from from multiple multiple superes superes Java Java does does not not support support multiple multiple inheritance inheritance CommunityMember Faculty Student Staff Alumnus Administrator Teacher The The important important relationship relationship between between a a sub sub and and its itssuper superis is the the IS-A IS-A relationship. relationship. The The IS-A IS-A relationship relationship must must exist exist if if inheritance inheritance is is used used properly. properly.

6 2. Defining Classes with Inheritance Case Study 1 1 Suppose we we want implement a which has two attributes, id idand, and some basic get- and set- methods for for the the attributes. We want now define a PartTime ; this will inherit these attributes and methods, but can also have attributes (hourlypay) and methods of of its its own (calculateweeklypay).

7 An inheritance relationship using UML Defining Classes with Inheritance +id string + string +(in N string, in E string) +setname(in N string) +getnumber() string +getname() string -hourlypay PartTime +PartTime(in N string, in E string, in H ) +sethourlypay(in H ) +gethourlypay() +calculateweeklypay(in c )

8 3. Inheritance and Member Accessibility We We use use the the following visual representation of of inheritance to to illustrate data data member accessibility.

9 The Effect of Three Visibility Modifiers

10 Accessibility of Super from Sub Everything except the the members of of the the Super is is visible from from a method of of the the Sub Sub.

11 The Protected Modifier The The modifier Protected makes a data data member or or method visible and and accessible to to the the instances of of the the and and the the descendant es (subes). Public data data members and and methods are are accessible to to everyone. Private data data members and and methods are are accessible only only to to instances of of the the.

12 An inheritance relationship using UML The Protected Modifier #id string # string +(in N string, in E string) +setname(in N string) +getnumber() string +getname() string The symbol # indicates the members -hourlypay PartTime +PartTime(in N string, in E string, in H ) +sethourlypay(in H ) +gethourlypay() +calculateweeklypay(in c )

13 Case Study 2 Defining Classes with Inheritance Suppose we we want want implement a roster that that contains both both undergraduate and and graduate students. Each Each student s record will will contain his his or or her her, three three test test scores, and and the the final finalcourse grade. The The formula for for determining the the course grade is is different for for graduate students than than for for undergraduate students.

14 Modeling Two Types of Students There are are two two ways to to design the the es to to model undergraduate and and graduate students. We We can can define two two unrelated es, one one for for undergraduates and and one one for for graduates. We We can can model the the two two kinds of of students by by using es that that are arerelated in in an an inheritance hierarchy. Two Two es are are unrelated if if they they are are not not connected in in an an inheritance relationship.

15 Classes for the Class Roster For the Class Roster sample, we design three es Student UndergraduateStudent GraduateStudent The Student will incorporate behavior and data common to both UndergraduateStudent and GraduateStudent objects. The UndergraduateStudent and the GraduateStudent will each contain behaviors and data specific to their respective objects.

16 4. Inheritance Hierarchy

17 5. Declaring Subes Student //DATA MEMBERS ; [[]] test; test; Members to be inherited are designated as GraduateStudent extends Student //DATA MEMBERS extends allows GraduateStudent to inherit Student

18 Implementation of Case Study 1 number; number; ; ; ( ( N, N, E) E) number number N; N; E; E; setname( setname( N) N) N; N; getnumber() getnumber() number; number; getname() getname() ; ; PartTime PartTime extends extends hourlypay; hourlypay; PartTime( PartTime( N, N, E, E, H) H) number number N; N; E; E; hourlypay hourlypay H; H; sethourlypay( sethourlypay( H) H) hourlypay hourlypay H; H; gethourlypay() gethourlypay() hourlypay; hourlypay; calculateweeklypay( calculateweeklypay( c) c) hourlypay hourlypay * * c; c;

19 import import java.util.scanner; java.util.scanner; PartTimeTest PartTimeTest static static main([] main([] args) args) Scanner Scanner input input new new Scanner(System.in); Scanner(System.in); number, number, ; ; pay; pay; hours; hours; PartTime PartTime emp; emp; PartTime test program. // // get get the the details details from from the the user user System.out.pr System.out.pr ( ( Number? ); Number? ); number number input.next(); input.next(); System.out.pr System.out.pr ( ( Name? ); Name? ); input.next(); input.next(); System.out.pr System.out.pr ( Hourly ( Hourly pay? ); pay? ); pay pay input.double(); input.double(); System.out.pr System.out.pr ( Hours ( Hours worked worked this this week? ); week? ); hours hours input.int(); input.int(); // // create create a a new new part-time part-time employee employee emp emp new new PartTime PartTime (number, (number,,, pay); pay); //display //display employee s employee s details, details, including including the the weekly weekly pay pay System.out.prln(); System.out.prln(); System.out.prln(emp.getName()); System.out.prln(emp.getName()); System.out.prln(emp.getNumber()); System.out.prln(emp.getNumber()); System.out.prln(emp.calculateWeeklyPay(hours)); System.out.prln(emp.calculateWeeklyPay(hours));

20 Implementation of Case Study 2 Student Student /** /** The The number number of of tests tests this this student student took took */ */ final final static static NUM_OF_TESTS NUM_OF_TESTS 3; 3; ; ; [] [] test; test; coursegrade; coursegrade; Student( Student( ) ) this this ("No ("No Name"); Name"); Student( Student( studentname) studentname) studentname; studentname; test test new new [NUM_OF_TESTS]; [NUM_OF_TESTS]; coursegrade coursegrade "****"; "****"; setscore( setscore( s1, s1, s2, s2, s3) s3) test[0] test[0] s1; s1; test[1] test[1] s2; s2; test[2] test[2] s3; s3; getcoursegrade( getcoursegrade( ) ) coursegrade; coursegrade; getname( getname( ) ) ; ; gettestscore( gettestscore( testnumber) testnumber) test[testnumber-1]; test[testnumber-1]; setname( setname( newname) newname) newname; newname; Dr. Salah Hammami GraduateStudent GraduateStudent extends extends Student Student /** /** * * students. students. Pass Pass if if total total > > 80; 80; otherwise, otherwise, No No Pass. Pass. */ */ GraduateStudent( GraduateStudent( na) na) na; na; computecoursegrade() computecoursegrade() total total 0; 0; for for ( ( i i 0; 0; i i < < NUM_OF_TESTS; NUM_OF_TESTS; i++) i++) total total + + test[i]; test[i]; if if (total (total > > 80) 80) coursegrade coursegrade "Pass"; "Pass"; else else coursegrade coursegrade "No "No Pass"; Pass"; UndergraduateStudent UndergraduateStudent extends extends Student Student UndergraduateStudent( UndergraduateStudent( na) na) na; na; computecoursegrade() computecoursegrade() total total 0; 0; for for ( ( i i 0; 0; i i < < NUM_OF_TESTS; NUM_OF_TESTS; i++) i++) total total + + test[i]; test[i]; if if (total (total / / NUM_OF_TESTS NUM_OF_TESTS > > 70) 70) coursegrade coursegrade "Pass"; "Pass"; else else coursegrade coursegrade "No "No Pass"; Pass";

21 Student test program Since both undergraduate and graduate students are enrolled in a, It seems necessary for us to declare two separate arrays, one for graduate students and another for undergraduate students GraduateStudent gradstudent [20]; UndergraduateStudent undergradstudent [20]; StudentTest static main([] args) GraduateStudent [] gradstudent new GraduateStudent[20]; UndergraduateStudent [] undergradstudent new UndergraduateStudent[20]; gradstudent[0] new GraduateStudent("Ramzi"); gradstudent[0].setscore (20, 30, 50); gradstudent[0].computecoursegrade(); System.out.prln(gradStudent [0].getCourseGrade( )); undergradstudent[0] new UndergraduateStudent ("Ahmed"); undergradstudent[0].setscore (10, 17, 13); undergradstudent[0].computecoursegrade(); System.out.prln(undergradStudent[0].getCourseGrade( ));

22 6. Inheritance and Constructors Unlike members of a super, constructors of a super are not inherited by its subes. You must define a constructor for a or use the default constructor added by the compiler. A sub uses a constructor from the base to initialize all the data inherited from the base In order to invoke a constructor from the base, it uses a special syntax SubClass extends SuperClass //DATA MEMBERS. // Constructors super ( );.

23 Inheritance and Constructors A call to the base constructor can never use the of the base, but uses the keyword super instead A call to super must always be the first action taken in a constructor definition An instance variable cannot be used as an argument to super

24 Inheritance and Constructors number; number; ; ; ( ( N, N, E) E) number number N; N; E; E;.. Call to super constructor to initialize members inherited from super PartTime PartTime extends extends hourlypay; hourlypay; PartTime( N, E, H) number N; E; hourlypay H; PartTime PartTime extends extends hourlypay; hourlypay; PartTime( PartTime( N, N, E, E, H) H) super (N, E); hourlypay H;..

25 Case Study 3 Inheritance Hierarchy of Class BankAccount 1 Bank + string - string #accnumber string -balance +branchname string BankAcount +BankAccount(in accnum string, in nam string, in bal ) +getname() string +getaccnumber() string #getbalancer() #setbalance(in bal ) +deposite(in amount ) #debit(in amount ) -sum(in a, in b ) 1..* -erestrate +Savings(in accnum, in nam, in bal, in rate ) +getinterest() +addinterest() +setinterestrate(in rate ) +display() Savings

26 Implementation of Case Study 3 BankAccount BankAccount accnumber; accnumber; ; ; balance; balance; branchname; branchname; BankAccount( BankAccount( number, number, bal, bal, na na,, branna) branna) accnumber accnumber number; number; balance balance bal; bal; na; na; branchname branchname branna; branna; getaccnumber() getaccnumber() accnumber; accnumber; sum( sum( a, a, b) b) a+b; a+b; copy(bankaccount copy(bankaccount client) client) accnumber accnumber client.accnumber; client.accnumber; client.; client.; balanceclient.balance; balanceclient.balance; branchname branchname client.branchname; client.branchname; getbalance() getbalance() balance; balance; setbalance( setbalance( bl) bl) balance balance bl; bl; getname() getname() ; ; deposite( deposite( amount) amount) balancesum(balance balancesum(balance,, amount); amount); debit( debit( amount) amount) if if (amount (amount > > balance) balance) System.out.prln("Sorry.. System.out.prln("Sorry.. you you cannot cannot debit debit the"+amount); the"+amount); else Dr. else balancebalance Salah balancebalance - Hammami - amount; amount; Savings Savings extends extends BankAccount BankAccount erestrate; erestrate; Savings( Savings( number, number, bal, bal, na, na, bankna, bankna, rate) rate) super(number, super(number, bal, bal, na, na, bankna); bankna); erestrate erestrate rate; rate; setinterestrate( setinterestrate( rate) rate) erestrate erestrate rate; rate; getinterestrate() getinterestrate() erestrate; erestrate; addinterest() addinterest() erest erest (getbalance()* (getbalance()* ersetrate ersetrate )/100; )/100; setbalance(getbalance() setbalance(getbalance() + + erest); erest); display() display() System.out.prln(branchName+getName()+accNumber System.out.prln(branchName+getName()+accNumber +getbalance()); +getbalance());

27 Bank Bank ; ; BankAccount BankAccount [] [] customer; customer; nbc; nbc; Bank( Bank( size, size, na) na) customer customer new new BankAccount[size]; BankAccount[size]; na; na; nbc0; nbc0; boolean boolean addcustomers(bankaccount addcustomers(bankaccount client) client) if if (nbc (nbc < < customers.length) customers.length) customers[nbc++] customers[nbc++] client; client; true; true; else else false; false; BankAccountTest BankAccountTest static static main([] main([] args) args) Savings Savings savacc savacc new new Savings("112233", Savings("112233", , , "Ahmed", "Ahmed", "AlMalaz",10.0); "AlMalaz",10.0); savacc.display(); savacc.display(); savacc.debit(100.0); savacc.debit(100.0); //--- //--- object object savacc savacc inherites inherites method method debit debit from from the the superclass superclass BankAccount BankAccount savacc.display(); savacc.display(); savacc.addinterest(); savacc.addinterest(); //--- //--- object object savacc savacc utilizes utilizes method method addinterset addinterset from from subclass subclass savacc.display(); savacc.display(); savacc.deposite(10.5); savacc.deposite(10.5); //--- //--- object object savacc savacc inherites inherites method method deposit deposit from from the the superclass superclass BankAccount BankAccount savacc.display(); savacc.display(); Execution Execution of of the the program program BankAccountTest BankAccountTest Branch Branch Name Name AlMalaz AlMalaz Custemer Custemer Ahmed Ahmed Accunt Accunt namber namber Balance Balance Branch Branch Name Name AlMalaz AlMalaz Custemer Custemer Ahmed Ahmed Accunt Accunt namber namber Balance Balance Branch Branch Name Name AlMalaz AlMalaz Custemer Custemer Ahmed Ahmed Accunt Accunt namber namber Balance Balance Branch Branch Name Name AlMalaz AlMalaz Custemer Custemer Ahmed Ahmed Accunt Accunt namber namber Balance Balance

28 Case Study 4 # string #id string Vehiccle +Vehicle(in n string, in d string) +set(in s string, in x string) +display() +...(in...) Car -seatnb -year -ncel +Car(in n string, in d string, in s, in y, in size ) +display() +isfull() bool +copycar(in ca Car) +addelement(in el CarElements) bool +PriceCar() +...(in...) 1 * -code string -price CarElements +CarElements(in c string, in p ) +CarElement(in E CarElements) +display() +...(in...) * 1 -nbc KsuCars +KsuCars(in size ) +display() +isempty() bool +searchcar(in ce string) +getcar(in nm string) Car +AveragePrice(in y ) +...(in...) +remove(in s string) bool

29 Question Implement all the es with all their methods using the following descriptions. Description of the different es Class Vehicle The method display () displays the and the id. +.. (in..) if you need an other methods in this you can add it. Class CarElements The method display () displays the code and the price. +.. (in..) if you need an other methods in this you can add it. You can t add another constructor. Class Car seatnb Number of seats year Production year of car ncel number of CarElements object currently in an object of the Car. And other attribute(s) deduced from the UML diagram. display () Displays all the attributes of an object Car. addelement (CarElements el) This method receives a CarElements object and adds it to the Car object. pricecar() Returns the sum of the CarElements price in an object of the Car. +.. (in..) if youneed an other methods in this you can add it. Class KsuCars nbc number of Car currently in an object of the KsuCar. And other attribute(s) deduced from the UML diagram. display () Displays all the attributes of an object KsuCars. search ( ce) This method receives a representing the of a Car object and s the array index of the car object. getcar ( nm) This method receives a representing the id of a Car object and s the Car object if it s exist. removecar ( s) Removes a Car according to its. It will a value true if the operation has been completed successfully, or false if not. AveragePrice( y) Calculates the average price of all car in an object of KsuCars that produced after the year y. +.. (in..) if youneed an other methods in this you can add it.