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Chapter 9

Chapter 9. Implementing Association Relationships. Objectives. In this chapter, you will: Identify association relationships on Bradshaw Marina’s class diagram Associate VB .NET classes in a one-to-one relationship Add functionality to the Boat class. Objectives. In this chapter, you will:

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Chapter 9

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  1. Chapter 9 Implementing Association Relationships Object-Oriented Application Development Using VB .NET

  2. Objectives In this chapter, you will: • Identify association relationships on Bradshaw Marina’s class diagram • Associate VB .NET classes in a one-to-one relationship • Add functionality to the Boat class Object-Oriented Application Development Using VB .NET

  3. Objectives In this chapter, you will: • Associate Dock and Slips in a one-to-many relationship • Add the Boat and Customer classes to the Slip example • Create and use an association class—Lease Object-Oriented Application Development Using VB .NET

  4. Identifying Association Relationships on Bradshaw Marina’s Class Diagram • Association relationships • Show how instances of classes are associated, or connected, to each other • Indicate that the system requires information about these associations • Can be used to navigate from instance to instance following the association Object-Oriented Application Development Using VB .NET

  5. Identifying Association Relationships on Bradshaw Marina’s Class Diagram • In a class diagram • An association relationship • Appears as a line connecting classes • Multiplicity of the association • Indicated by numbers written at both ends of the line Object-Oriented Application Development Using VB .NET

  6. Identifying Association Relationships on Bradshaw Marina’s Class Diagram • Association relationships in the Bradshaw class diagram: • A customer owns a boat • A boat is owned by a customer • A boat is assigned to a slip • A slip contains a boat • A dock contains many slips • A slip is attached to a dock • A slip is leased to a customer (Lease is an association class) • A customer leases a slip (Lease is an association class) Object-Oriented Application Development Using VB .NET

  7. Identifying Association Relationships on Bradshaw Marina’s Class Diagram Object-Oriented Application Development Using VB .NET

  8. Identifying Association Relationships on Bradshaw Marina’s Class Diagram • Lease class • An example of an association class • Exists because of the relationship between a slip and a customer • In the class diagram • Shown as a class connected by a dashed line to an association between Slip and Customer Object-Oriented Application Development Using VB .NET

  9. Associating VB .NET Classes in a One-to-One Relationship • Association relationship between Customer and Boat • Has two “directions” • A customer owns a boat • A boat is owned by a customer • Each direction of the relationship • Must be defined separately by the system developer • Must be handled separately with VB .NET Object-Oriented Application Development Using VB .NET

  10. Associating VB .NET Classes in a One-to-One Relationship • To implement an association relationship in VB .NET • Use a reference variable as an attribute of a class • A reference variable points to an actual instance Object-Oriented Application Development Using VB .NET

  11. Associating VB .NET Classes in a One-to-One Relationship Object-Oriented Application Development Using VB .NET

  12. Associating VB .NET Classes in a One-to-One Relationship • A Customer reference variable • Points to a Customer instance • If added as an attribute in the Boat class, each Boat instance can • Point to a Customer instance • Invoke the customer’s methods Object-Oriented Application Development Using VB .NET

  13. Associating VB .NET Classes in a One-to-One Relationship • A Boat reference variable • Points to a Boat instance • If added as an attribute in the Customer class, each Customer instance can • Point to a Boat instance • Invoke the boat’s methods Object-Oriented Application Development Using VB .NET

  14. Modifying the Customer Class • Modifying the Customer class implements one direction of the association relationship • From Customer to Boat • theBoat attribute • A Boat reference variable • Added to the Customer class • Used to implement a one-to-one association relationship with the Boat class Object-Oriented Application Development Using VB .NET

  15. Modifying the Customer Class • Accessor methods • SetBoat • Accepts a Boat reference as a parameter • Assigns the reference to the attribute • GetBoat • Returns the Boat reference Object-Oriented Application Development Using VB .NET

  16. Modifying the Customer Class • Constructor • Sets the Boat reference variable to Nothing using the SetBoat method • Once Customer instance is created • Boat reference variable can be set to an actual Boat reference Object-Oriented Application Development Using VB .NET

  17. Modifying the Boat Class • Modifying the Boat class implements the other direction of the association relationship • A boat is owned by a customer • theCustomer attribute • A Customer reference variable • Added to the Boat class • Used to implement a one-to-one association relationship with the Customer class Object-Oriented Application Development Using VB .NET

  18. Modifying the Boat Class • Accessor methods • GetCustomer • Returns the Customer reference • SetCustomer • Accepts a Customer reference as a parameter • Assigns the reference to the attribute Object-Oriented Application Development Using VB .NET

  19. Adding Functionality to the Boat Class • Functionality of classes that have association relationships can be increased • AssignBoatToCustomer custom method • Added in Boat • Establishes the association between Boat and Customer in both directions in one step Object-Oriented Application Development Using VB .NET

  20. Adding Functionality to the Boat Class • Mandatory association between Boat and Customer • Possible because • Bradshaw Marina does not want to keep information about a boat if its owner is not a customer • Done by • Adding a Customer reference parameter to the Boat constructor Object-Oriented Application Development Using VB .NET

  21. Adding Functionality to the Boat Class • Modified Boat TellAboutSelf method • Returns information about • Boat • Customer • Possible because • A boat must be associated with a customer Object-Oriented Application Development Using VB .NET

  22. Associating Docks and Slips: A One-to-Many Association Relationship • Association relationship between Slip and Dock • Two directions of the relationship • Association relationship between Slip and Dock • One-to-one • A slip is attached to a dock • Association relationship between Dock and Slip • One-to-many • A dock contains many slips Object-Oriented Application Development Using VB .NET

  23. Associating Docks and Slips: A One-to-Many Association Relationship • To implement • A one-to-one association relationship between Slip and Dock • Use the technique used to implement the Customer and Boat associations • A one-to-many association relationship between Dock and Slip • Requires that a dock instance have reference variables for more than one slip • Use an ArrayList in the Dock class to hold many Slip reference variables Object-Oriented Application Development Using VB .NET

  24. Associating Docks and Slips: A One-to-Many Association Relationship • ArrayList class • Can be used to instantiate a container that can hold many reference variables • Has methods which can be used to • Add Slip references • Retrieve Slip references Object-Oriented Application Development Using VB .NET

  25. Introducing the Dock Class • Dock class • Four previous attributes • An ID number • A location • Two Boolean variables indicating • Whether the dock has electricity • Whether the dock has water • Fifth attribute • slips • An ArrayList • Implements the one-to-many association relationship Object-Oriented Application Development Using VB .NET

  26. Introducing the Dock Class • Dock class constructor • Sets values for the four attributes • Instantiates the new ArrayList • Assigns the new ArrayList to the slips attribute • GetSlips • A getter method • Returns the slips reference variable Object-Oriented Application Development Using VB .NET

  27. Introducing the Dock Class • AddSlip custom method • Used to add a slip to the dock • Invoked by the Slip AddSlipToDock method • Contains the slips.Add(aSlip) statement • Used to add a Slip reference to the ArrayList referenced by the variable slips Object-Oriented Application Development Using VB .NET

  28. Associating the Slip Class with Dock • Modifications to the Slip class to implement the mandatory one-to-one association relationship • theDock attribute • A Dock reference variable • Accessor methods for the Dock reference attribute Object-Oriented Application Development Using VB .NET

  29. Associating the Slip Class with Dock • Modifications to the Slip class (Continued) • Modified constructor • Expects a Dock reference parameter • Result: When a slip is instantiated, it must be associated with a dock • Invokes the slip’s AddSlipToDock method • AddSlipToDock method establishes the association in both directions by • Invoking the dock’s AddSlip method using the Me keyword Object-Oriented Application Development Using VB .NET

  30. Associating the Slip Class with Dock • Modifications to the Slip class (Continued) • A TellAboutSelf method • Returns information about • The slip • The slip’s dock Object-Oriented Application Development Using VB .NET

  31. Adding the Boat and Customer Classes to the Slip Example • Association relationship between Slip and Boat • Modifications to the Slip class • A Boat reference attribute • Accessor methods • GetBoat • SetBoat • Modifications to the Boat class • A Slip reference attribute • Accessor methods • AssignBoatToSlip method Object-Oriented Application Development Using VB .NET

  32. Adding the Boat and Customer Classes to the Slip Example • To include the Customer class in this example • Boat class does not need to be modified • It is already designed to associate with a customer • Given a Customer reference • Can navigate to find • The customer’s boat • The boat’s slip • The slip’s dock Object-Oriented Application Development Using VB .NET

  33. Adding the Boat and Customer Classes to the Slip Example • Given a Dock reference • Can navigate to • Each slip • The slip’s boat • The customer who owns the boat Object-Oriented Application Development Using VB .NET

  34. Creating and Using an Association Class – Lease • Lease class • An association class • A Lease is like an association between a customer and a slip, but with attributes for • Start date • End date • Amount of lease, and so on • Subclasses • AnnualLease • DailyLease Object-Oriented Application Development Using VB .NET

  35. Creating and Using an Association Class – Lease • Modifications to the Lease superclass • A Slip reference attribute • A Customer reference attribute • Accessor methods • AnnualLease class • A subclass of Lease • Inherits the association between • Lease and Slip • Lease and Customer Object-Oriented Application Development Using VB .NET

  36. Creating and Using an Association Class – Lease • No modifications needed for the Boat class • Reason: Boat is not directly associated with Lease • Modifications to the Customer class • A Lease reference attribute • Accessor methods Object-Oriented Application Development Using VB .NET

  37. Creating and Using an Association Class – Lease • Modifications to the Slip class • A Lease reference attribute • Accessor methods • LeaseAnnualSlip method • Creates an AnnualLease instance Object-Oriented Application Development Using VB .NET

  38. Summary • Association relationships are shown on the class diagram as lines connecting classes • Association relationships are implemented in two directions that must be considered separately • Association relationships can be optional or mandatory • One-to-one association relationships are implemented by including a reference variable as an attribute in one class that points to an instance of another class Object-Oriented Application Development Using VB .NET

  39. Summary • One-to-many association relationships are implemented using an ArrayList that contains a collection of reference variables • Association relationships can be directly navigated by writing one statement with multiple method calls that are executed from left to right • An association class exists because of a relationship between two classes, such as Lease between Slip and Customer Object-Oriented Application Development Using VB .NET

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