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Ooad sequence diagram lecture


object-oriented programming

object-oriented programming

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  • 1. By Nadeem MahmoodDepartment of Computer Science University Of Karachi
  • 2. Interaction DiagramsInteraction diagrams describe exemplary how groups of objects collaborate in some behavior.An interaction diagram typically captures the behavior of a single use case.Interaction diagrams do not capture the complete behavior, only typical scenarios.
  • 3. Types of Interaction Diagrams There are two types of interaction diagrams:Sequence diagrams emphasize the order or concurrency of the interactions.Collaboration diagrams emphasize the interacting objects.
  • 4. Behavior of the “order” use case:A customer orders several products.The (sub-)orders (“order lines”) for each product are preparedseparately.For each product check the stock.• If the product is in stock, remove requested amount from stock.• If the product stock falls below a predefined level, reorder it.
  • 5. ObjectObject naming:  syntax: [instanceName][:className] myBirthdy :Date  Name classes consistently with your class diagram (same classes).  Include instance names when objects are referred to in messages or when several objects of the same type exist in the diagram.The Life-Line represents the object’s life during the interaction
  • 6. MessagesAn interaction between two objects is performed as a message sent from one object to another (simple operation call, Signaling, RPC)If object obj1 sends a message to another object obj2 some link must exist between those two objects (dependency, same objects)
  • 7. Messages (Cont.)A message is represented by an arrow between the life lines of two objects.  Self calls are also allowed  The time required by the receiver object to process the message is denoted by an activation-box.A message is labeled at minimum with the message name.  Arguments and control information (conditions, iteration) may be included.
  • 8. Return ValuesOptionally indicated using a dashed arrow with a label indicating the return value. Don’t model a return value when it is obvious what is being returned, e.g. getTotal() Model a return value only when you need to refer to it elsewhere, e.g. as a parameter passed in another message. Prefer modeling return values as part of a method invocation, e.g. ok = isValid()
  • 9. Synchronous MessagesNested flow of control, typically implemented as an operation call. The routine that handles the message is completed before the caller resumes execution. :A :B doYouUnderstand() return Caller yes (optional) Blocked
  • 10. Object CreationAn object may create another object via a <<create>> message. Preferred :A :B :A <<create>> <<create>> :B Constructor
  • 11. Object DestructionAn object may destroy another object via a <<destroy>> message.  An object may destroy itself.  Avoid modeling object destruction unless memory management is critical. :A :B <<destroy>>
  • 12. Why not just code it? Sequence diagrams can be somewhat close to the code level. So why not just code up that algorithm rather than drawing it as a sequence diagram?  a good sequence diagram is still a bit above the level of the real code (not EVERY line of code is drawn on diagram)  sequence diagrams are language-agnostic (can be implemented in many different languages  non-coders can do sequence diagrams  easier to do sequence diagrams as a team  can see many objects/classes at a time on same page (visual bandwidth)17
  • 13. Lifetime of objectscreation: arrow with new written above it notice that an object created after the start of the scenario appears lower than the othersdeletion: an X at bottom of objects lifeline Java doesnt explicitly delete objects; they fall out of scope and are garbage-collected 18
  • 14. Indicating selection and loopsframe: box around part of a sequence diagram to indicate selection or loop if -> (opt) [condition] if/else -> (alt) [condition], separated by horiz. dashed line loop -> (loop) [condition or items to loop over] opt [balance 0] <> alt [balance 100 ] < .00 [balance 100 ] >= .00 loop [balance 0] <19
  • 15. Reference: Object-Oriented Analysis and DesignJ.W. Schmidt, F. Matthes, TU Hamburg-Harburg
  • 16. Reference: Object-Oriented Analysis and DesignJ.W. Schmidt, F. Matthes, TU Hamburg-Harburg
  • 17. Sequence diag. from use case26