http:www.cs.bgu.ac.iloosd042

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• ???? 2004
• http//www.cs.bgu.ac.il/oosd042

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• UML
• Application Frameworks
• The GUI framework
• Design patterns
• Designing concurrent objects
• Designing components
• Applets and Servlets

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• Xiaoping Jia Object-oriented software design
  in Java , Addison-Wesley, 2000.
• P. Stevens Using UML , Pearson Education,
  2000.

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Object Oriented Concepts

• Refresh Course

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Evaluating Systems

• Dependency
• Module A depends on module B if a change in B may
  cause a change in A.
• Module A is a client of module B.
• Module B is a server of module A.
• Note that circular dependency may exist

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Evaluating Systems (cont)

• Coupling
• Dependency is sometimes known as coupling.
• High coupling A system with many dependencies.
• A good system has low coupling changes in one
  part are less likely to propagate.

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Evaluating Systems (cont)

• Encapsulation low coupling
• Interface
• encapsulate knowledge about the module.
• Syntactic aspects of dependency
• Semantic dependency
• The module specification what clients can assume.

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Evaluating Systems (cont)

• Abstraction high cohesion
• When a client doesnt need to know more than the
  interface.
• (Encapsulation is when the client isnt able to
  know)

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Components

• A unit of reuse and replacement.
• Pluggable.

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Objects

• Our view of objects

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What is an object?

• A thing you interact with.
• Send messages to an object (method).
• The object react to messages.
• An object behaves according to its internal
  state.
• State the data the object encapsulates.
• Attributes.
• Behavior
• The way an object acts and reacts in terms of
  message passing and state changes.
• Identity (name)

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The Object (public) Interface

• Defines the messages an object can accept.
• An object also have an internal (private)
  interface.
• An object may send messages to itself.

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Classes?!

• A class describe a set of object with an
  equivalent role.
• Defines
• Methods
• Attributes
• Creating a new object of a class is called
  instantiating. The result is an instance.
• A class is considered an object factory.
• Why classes?
• Write once.
• Single copy of the code (multiple data).

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Inheritance

• Objects
• Lecturer
• DirectorOfStudies (a special type of lecturer)
• DirectorOfStudies is a subclass (extension) of
  Lecturer.
• It can
• Override methods or attributes
• Inherit methods of the super class.
• Have new methods.

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Polymorphism and Dynamic Binding

• Polymorphism An entity may have several types
  (super class, subclass or interface).
• Binding is identifying the code to execute as a
  result of a message.
• Dynamic? because at runtime we need to find the
  actual type of the object.

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UML

• Unified Modeling Language

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An Object

• First we need to identify the objects in the
  system.
• Object has a name, attributes and operations.

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Object Associations

• Called links (between objects)
• Class A and class B are associated if
• An object of A sends a message to an object of B.
• An object of A creates an object of B.
• An object of A has an attribute that is a value
  of B.
• An object of A receives a message with an object
  of B as an argument.

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Object Hierarchy (generalization)

• A shop is selling
• Books
• Music CDs
• Software
• All the above are Item.
• An arrow representgeneralization.

Item title publisher yearPublished ISDB price
Book author edition volume
MusicCD artist volume
Software version
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Object Hierarchy (generalization)

• Inheritance is an implementation of
  generalization.
• Example Item and Book
• Book is a subclass of Item
• Consider the following
• Example List and AddressBook
• Q Should AddressBook extends List? or should
  List be an attribute in AddressBook.

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Aggregation and Composition

• Open diamond describe aggregation when an
  object is part of (and may be part of others).
• Composition when the whole strongly owns its
  part. (denoted by a filled diamond)

The numbers on the sides of the line denotes
occurrences.
ItemOrder item quantity
0..
ShoppingCart
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Example (of associations)
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Example Singleton class

• public class Singleton
• public static Singleton getInstance()
• if ( _theInstance null )
• _theInstance new Singleton()
• return _theInstance
• protected Singleton()
• // .....
• //
• // .... methods ....
• //
• private static Singleton _theInstance null

Singleton static Singleton _theInstance static
getInstance() Singleton operation()
void getData() int
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Use Case Models

• Documents the system behavior from the users
  points of view.
• It helps with
• Finding requirements.
• Validating systems.
• Planning development iterations.
• An actor is a users of the system

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Example Use Case in A Library
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Sequence Diagrams

• Shows both actors and objects that take place in
  a behavior of the system.
• Describes the sequence of state changes (and
  therefore, behavior) of the code (and not data or
  objects).
• Resembles finite automates.

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Example Borrow a Book
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Message Sending Options
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State Diagrams

• Describe how to model the object decision as a
  result of a message.
• Example A state diagram of a Copy (of book)
• A copy has an attribute
• onShelf Boolean
• values on load / on the shelf

Initial State
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State Diagram (cont)

• States as boxes
• Transitions as arrows
• Events are shown as messages on the arrows
• Start marker is a black blob

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State Diagram (cont)

• Adding actions (as a result of messages)
• Actions (after the /) shows what action is
  taken after the event.
• Actions may be written as entry actions inside
  the state box (or exit actions).
• Useful when many transitions leads to a state.

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State Diagram (cont)

• Guards - adding conditions to events
• A book (with many copies) can (or cant) be
  borrowed.

If last copy then change state