Association - Direction. Association Implementation. Association Example. Unidirectional Association - Example

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1 Association - Direction Unidirectional Association - Example Unidirectional One object can send messages to the other, but this other object cannot send messages back and has no knowledge about the object referring to it. Bidirectional - Both objects know about each other and messages can be passed in either direction. has exactly one Guarantor. has to access (invoke methods) on the Guarantor. The guarantor has no knowledge (cannot invoke methods) of the account. Guarantor 2 Association Example Unidirectional association from to DebitCard. has exactly zero or one DebitCard 0.. DebitCard public class private DebitCard thecard; public String getcardnumber() return thecard.getnumber(); public void setcard(debitcard card) thecard = card; public void removecard() thecard = null; sends a message to DebitCard 3 4 public class DebitCard private String thecardnumber; Unidirectional association from to Guarantor has exactly one Guarantor public String getnumber() return thecard.number; Guarantor 5 6

2 public class public (Guarntor g) if ( g == null) // throw error the guarantor =g; public Guarantor getguarantor() return theguarantor; private Guarantor theguarantor; Unidirectional association from Manager to Manager can supervise a number of accounts but it is never necessary to know who is managing the accounts. Manager * 7 8 public class Manager public void add ( acc) thes.addelement(acc); public void remove( acc) thes.removeelement(acc); private Vector thes; Bidirectional association from to DebitCard. can send messages to DebitCard and DebitCard can send messages to has exactly zero or one DebitCard 0.. DebitCard 9 0 I mplementation public class private DebitCard thecard; public DebitCard getcard() public void setcard(debitcard card) public void removecard() public class DebitCard private the; public DebitCard( a) public get() Implementation provides the data members necessary to store bidirectional links. However creating the objects require multiple step and does not guarantee referential integrity. acc = new () DebitCard ca = new DebitCard(acc) acc.setcard(ca) acc = new () acc2 = new () DebitCard ca = new DebitCard(acc2) acc.setcard(ca) 2

3 I mplementation 2 public class private DebitCard thecard; public DebitCard getcard() public void setcard(debitcard card) public void removecard() public void addcard() thecard = new DebitCard(this) public class DebitCard private the; DebitCard( a) the = a; public get() Implementation 2 ensures referential integrity. acc = new () acc.addcard() 3 4 Class Relationships Association Generalization Realization Generalization (Inheritance) Child class is a special case of the parent class SuperClass SubClass SubClass2 5 6 Generalization (Inheritance) e.g. Inheritance - Implementation public class Graphic public class Graphic extends 7 8

4 Abstract Class Abstract Methods (Operations) Shape draw() Shape Rectangle Rectangle draw() draw() 9 20 Notes If the class is defined as Abstract no objects of the class can be instantiated. If at least one method in a class is defined as abstract then the class is abstract. In UML an abstract class and operations are denoted in italics. Abstract class and method Implementation public abstract class Shape public abstract draw(); //declare without implementation public class public draw() Class Relationships Association Generalization Realization Realization- Interface Interface is a set of operation the class carries out Keyboard brandname numofkeys ctl() pagedown() <<interface>> TypeWriter keystroke() OR Keyboard brandname numofkeys ctl() pagedown() TypeWriter 23 24

5 Realization - Implementation Class Relationships public interface TypeWriter void keystroke() public class KeyBoard implements TypeWriter public void keystroke() Association Generalization Realization cont Change in specification of one class can change the other class. This can happen when one class is using another class. Move(p:Point) Point relationship can be used to show relationships between classes and objects. < <instanceof> > < < instanceof> > circlea: circleb: Class Diagrams Class Diagram - Example The UML class diagram consists of several Classes, connected with Relationships. Draw a class diagram for a information modeling system for a school. The classes are School, Department, Student, Course, Instructor

6 Class Diagram Example Object Diagram * School has..* Department..* Object Diagram shows the relationship between objects. member offeredby assignedto Unlike classes objects have a state. *..*..* attends teaches Student Course Instructor * * *..* 3 32 Object Diagram - Example c: Company d: Department name= Sales d2: Department name= R&D manager p: Persont name= John employee p2: Person name= David 33