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OOP Review

OOP Review. CS 124. Object-Oriented Programming Revisited. Key OOP Concepts Object, Class Instantiation, Constructors Encapsulation Inheritance and Subclasses Abstraction Reuse Polymorphism, Dynamic Binding Object-Oriented Design and Modeling. Object.

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OOP Review

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  1. OOP Review CS 124

  2. Object-Oriented ProgrammingRevisited • Key OOP Concepts • Object, Class • Instantiation, Constructors • Encapsulation • Inheritance and Subclasses • Abstraction • Reuse • Polymorphism, Dynamic Binding • Object-Oriented Design and Modeling

  3. Object Definition: a thing that has identity, state, and behavior • identity: a distinguished instance of a class • state: collection of values for its variables • behavior: capability to execute methods * variables and methods are defined in a class

  4. Class Definition: a collection of data (fields/ variables) and methods that operate on that data • define the contents/capabilities of the instances (objects) of the class • a class can be viewed as a factory for objects • a class defines a recipe for its objects

  5. Instantiation • Object creation • Memory is allocated for the object’s fields as defined in the class • Initialization is specified through a constructor • a special method invoked when objects are created

  6. Encapsulation • A key OO concept: “Information Hiding” • Key points • The user of an object should have access only to those methods (or data) that are essential • Unnecessary implementation details should be hidden from the user • In Java/C++, use classes and access modifiers (public, private, protected)

  7. Inheritance • Inheritance: • programming language feature that allows for the implicit definition of variables/methods for a class through an existing class • Subclass relationship • B is a subclass of A • B inherits all definitions (variables/methods) in A

  8. Abstraction • OOP is about abstraction • Encapsulation and Inheritance are examples of abstraction • What does the verb “abstract” mean?

  9. Reuse • Inheritance encourages software reuse • Existing code need not be rewritten • Successful reuse occurs only through careful planning and design • when defining classes, anticipate future modifications and extensions

  10. Polymorphism • “Many forms” • allow several definitions under a single method name • Example: • “move” means something for a person object but means something else for a car object • Dynamic binding: • capability of an implementation to distinguish between the different forms during run-time

  11. Building Complex Systems • From Software Engineering:complex systems are difficult to manage • Proper use of OOP aids in managing this complexity • The analysis and design of OO systems require corresponding modeling techniques

  12. Object-Oriented Modeling • UML: Unified Modeling Language • OO Modeling Standard • Booch, Jacobson, Rumbaugh • What is depicted? • Class details and static relationships • System functionality • Object interaction • State transition within an object

  13. Some UML Modeling Techniques • Class Diagrams • Use Cases/Use Case Diagrams • Interaction Diagrams • State Diagrams

  14. Example:Class Diagram Borrower Book 0..3 0..1 currBorr bk[] public class Borrower { Book bk[]; … public Borrower() { bk = new Book[3]; } } public class Book { Borrower currBorr; … }

  15. Example:Use Case Diagram LIBRARY SYSTEM Facilitate Checkout Search for Book Borrower Librarian Facilitate Return

  16. Example:Interaction Diagram 2: isAvailable() Checkout Screen :Book 1: borrowAllowed() 3: borrowBook() 4: setBorrower() :Borrower

  17. Example:State Diagram (Book) start Reserved Borrowed New Librarian activates book as available Borrower returns book Available

  18. Object-Oriented Design Models • Static Model • Class Diagrams • Dynamic Model • Use Cases, Interaction Diagrams, State Diagrams, others

  19. OO Static Model • Classes and Class Diagrams • Relationships • Association • Aggregation/Composition • Inheritance • Dependencies • Attribute and Method names

  20. OO Dynamic Model • Goal: Represent • Object behavior • Object interaction • Traditional/Procedural Dynamic Modeling • Data Flow Diagrams (DFDs) • Problem: Processes separate from data • Need modeling notation that highlight tight relationship between data & processes

  21. DFD Example(Inventory Management) Accept and Post Delivery Delivery info Transaction Item Master

  22. OO Counterpart:Object Interaction new (delivery info) Encoder :Transaction post (item count) :Item Master

  23. Building anOO Dynamic Model • Identify use cases • Describe each use case through an interaction diagram • For more complex objects, provide a state diagram per class • Derive implied methods (and attributes)

  24. What’s Next? • Need to understand the notation • Make sure it helps the software development process • When to use the UML techniques • Primarily when specifying OO design • Formal means of communication across the different software development stages

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