Java Inheritance. Class ADT (Abstract Data Type) Interface. Classes implement the concept of ADT: Interfaces define interaction contracts: Rui Moreira

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1 Java Iheritace Rui Moreira Class ADT (Abstract Data Type) Classes implemet the cocept of ADT: Provide a coheret represetatio for the declaratio of structured data types ad also the code for maipulatig those data types, i.e., associate i the same cocept (class) the member variables (attributes) ad the member fuctios (methods) Data ad code are o loger separated cocepts, i.e., we may thik o data objects with implicit behaviour ad that may chage themselves we o loger have the separatio betwee data structures ad the fuctios for maipulatig those structures (as with C or Pascal) Rui Moreira 2 Iterface Iterfaces defie iteractio cotracts: Iterfaces are mechaisms/devices that objects may use to iteract (e.g., we iteract with a TV through its public iterface cotrols) A iterface is a collectio of methods which defie the public behaviour exposed by several object (e.g., get, set, move, area, etc.) Iterfaces expose classes/objects behaviour without revealig its iteral implemetatio/details - ecapsulatio A class that implemets a iterface agrees to implemet all the behaviour defied by the iterface methods - cotract Rui Moreira 3 1

2 Iterface Defiitio Iterface q defies the sigature of a set of public methods q method defitio has o body/implemetatio /** AccoutMoeyI: defies methods for maipulatig the Accout moey */ public iterface AccoutMoeyI { public void whidraw(log amout); public void deposit(log amout); public log balace(log amout); /** AccoutRelatioI: defies methods for gettig objects related with Accout */ public iterface AccoutRelatioI { public Cliet getcliet(); public BakMaager getbakmaager(); AccoutMoeyI (from bak) whi deposit( ) balace( ) AccoutRelatioI getcliet( ) getbakmaager( ) Rui Moreira 4 Multiple Iterface Iheritace // A class ca implemet several iterfaces public class AccoutImpl implemets AccoutMoeyI, AccoutRelatioI { // Some attributes here... // The all methods must be implemeted public void whidraw(log amout){ public void deposit(log amout){ public log balace(log amout) ){ public Cliet getcliet() ){ public BakMaager getbakmaager() ){ AccoutMoeyI AccoutRelatioI (from bak) getcliet( ) whi getbakmaager( ) deposit( ) getbalace( ) AccoutImpl (from bak) balace : log accoutnumber : Strig AccoutImpl( ) Rui Moreira 5 Class Iheritace A Java class ca iherit (exted) aother class: Employee ame : Strig = "" /** Super-class Employee: birth : Date = ull salary : float represets a geeric employee */ Employee( ) public class Employee { getname( ) public Strig ame = ; getbirth( ) setbirth( ) private Date birth = ull; getsalary( ) setsalary( ) private float salary; public Employee(Strig, Date b, float s) { /*... */ Maager Salesma subordiates[ ] : Employee zoe : Strig = ull /** Sub-class Maager: Maager( ) Salesma( ) represets a specific employee */ getsubordiates( ) getzoe( ) public class Maager exteds Employee { private Employee subordiates[]; public Maager(Strig, Date b, float s, Employee[] sub) { /*... */ Rui Moreira 6 2

3 Class Iheritace Java allows oly sigle class iheritace, i.e., exted oly 1 class at a time (because of the diamod problem) The subclass iherits oly public attributes ad public methods (i.e., private attributes ad methods of super-class are ot accessible to subclass) Costructors are ot iherited, therefore the subclass must implemet its ow costructors ad explicitly call super-class costructors Rui Moreira 7 Operators: this ad super Java provides 2 operators: q q this: for referecig the class/object itself super: for referecig the super-class/object /** Sub-class Employee: represets a geeric employee */ public class Employee { /* Atributes */ public Strig ame = ; private Date birth = ull; private float salary; public Employee(Strig, Date b, float s) { this.ame = ; // SET OBJECT ATRIBUTE ame to this.birth = b; // SET OBJECT ATRIBUTE birth to b this.salary = s; // SET OBJECT ATRIBUTE salary to s Rui Moreira 8 Operators: this ad super Java provides 2 operators: q this: for referecig the class/object itself q super: for referecig the super-class/object public class Maager { private Employee subordiates[]; public Maager(Strig, Date b, float s, Employee[] sub) { super(, b, s); // EXPLICITLY CALL SUPER-CLASS CONSTRUCTOR this.subordiates = sub; /** Aother costructor */ public Maager(Strig, Date b, float s, Employee[] sub) { super.ame = ; // WE MAY SET PUBLIC ATRIBUTES //super.birth = b; NOT ALLOWED TO SET PRIVATE ATTRIBUTES!!!! super.setbirth(b); // ALTERNATIVELLY USE PUBLIC METHODS super.setsalary(s);// SET PRIVATE ATTRIBUTE VIA PUBLIC METHOD this.subordiates = sub; Rui Moreira 9 3

4 Object Polymorphism A object ca take several shapes // Variable emp is of type Employee Employee emp = ull; // Set referece to a ew Maager emp = ew Maager( Joh, ew Date(2, 08, 1980), 1000, arrayemp); // We CAN ACCESS all attributes/methods of Employee s = emp.getsalary(); // THIS IS ALLOWED!!!! // But CANNOT ACCESS attributes/methods of Maager // because emp is of type Employee arraysubord = emp.getsubordiates(); // THIS IS NOT ALLOWED!!!! // Same referece variable ca poit to a differet object emp = ew Salesma( Mary, ew Date(2, 08, 1980), 1000, Porto ); Rui Moreira 10 Cast Explicit cast: force a object to be of a give type // We CAN ACCESS attributes/methods of Maager // by castig/maskig emp to Maager subordiates = ((Maager)emp).getSubordiates(); // ALLOWED!!!! // We CAN ALSO ACCESS attributes/methods of Salesma // by castig/maskig the object (emp) to Salesma zoe = ((Salesma)emp).getZoe(); // ALSO ALLOWED!!!! NB: we CAN ONLY CAST objects that have/iherit the same base-type (i.e., same super-class). we CANNOT CAST betwee differet types of objects (i.e., which do ot share same super-class)!! Rui Moreira 11 Cast Explicit cast: restore the fucioality of a geeric object // Geeric object ca poit to ay kid of object Object obj = ew Rectagulo(2, 2, 4, 1); if (obj istaceof Rectagulo){ // CAST - Force rec to poit to a object Rectagulo Rectagulo rec = (Rectagulo)obj; // Now we ca access the attributes/methods of Rectagulo iside = rec.isiside(1, 1); Rui Moreira 12 4

5 Object Polymorphism istaceof - check istace type // pritifo(): prits iformatio about a give Employee // istace which depeds o its type public void pritifo(employee e){ if (e istaceof Employee) { e.descriptio(); // Prits employee ifo else if (e istaceof Maager) { e.descriptio(); // Prits maager ifo // Obtai maager subordiates sub = ((Maager)e).getSubordiates(); else if (e istaceof Salesma) { e.descriptio(); // Prits salesma ifo // Obtai Salesma zoe zoe = ((Salesma)e).getZoe(); Maager subordiates[ ] : Employee Maager( ) getsubordiates( ) Employee ame : Strig = "" birth : Date = ull salary : float Employee( ) getname( ) getbirth( ) setbirth( ) getsalary( ) setsalary( ) Salesma zoe : Strig = ull Salesma( ) getzoe( ) Rui Moreira 13 Method Polymorphism - Overload Overload methods: q the same method ame ca be used to idetify/implemet differet methods q each of the methods must have differet parameters q each method ca have the same or differet retur values public class PritClass { // Same method ame with differet parameters/argumets public void prit(it i){ System.out.prit( i = +i); public void prit(float f){ System.out.prit( f = +f); public void prit(strig s){ System.out.prit( s = +s); Rui Moreira 14 Method Polymorphism Override Override Methods (redefie behaviour of super-class methods): q the sub-class may add ew methods to the super-class but ca also redefie/override methods of the super-class (chage the behaviour of existig methods) // Method descriptio() is provided by Employee // ad overridde by Maager ad Salesma to add specific ifo public class Maager { public Strig descriptio(){ // Add additioal Maager ifo retur super.descriptio()+ : +this.subordiates.legth; public class Salesma { public Strig descriptio(){ // Add additioal Salesma ifo retur super.descriptio()+ : +this.zoe; Rui Moreira 15 5

6 Exercises Implemet the followig class diagram (NB: you may chage the classes already defied i previous examples/slides, e.g., Rectagulo, Triagulo, Circulo) Poto x : it = 0 y : it = 0 Poto( ) getx( ) gety( ) setx( ) 1..* sety( ) drawpoto( ) exteds Rectagulo upleftpoto : Poto = ull dowrightpoto : Poto = ull Rectagulo( ) getupleftpoto( ) getdowrightpoto( ) setupleftpoto( ) setdowrightpoto( ) isiside( ) area( ) tostrig( ) GeoFigureI getcolor( ) chagecolor( ) tostrig( ) implemets GeoFigure color : it exteds Circulo ceterpoto : Poto = ull diameter : it = 0 getceterpoto( ) getdiameter( ) setceterpoto( ) setdiameter( ) isiside( ) area( ) tostrig( ) exteds Triagulo uppoto : Poto = ull dowpoto : Poto = ull middlepoto : Poto = ull getuppoto( ) getdowpoto( ) getmiddlepoto( ) setuppoto( ) setdowpoto( ) setmiddlepoto( ) isiside( ) area( ) tostrig( ) Rui Moreira 16 6