Object Behaviours UML Statecharts

Transcription

1 Object Behaviours UML Statecharts Software Requirements and Design CITS 4401 Lecture 5 Based on Ch 5 Lecture Notes by Bruegge & Dutoit

2 Finite state machine flip switch on light off light on flip switch off

3 Finite state machine State flip switch on Transition light off light on flip switch off Event

4 Ex 1. Interaction with my PC (1) ctrl-alt-del logged off login screen confirm-logout username-passwd logout screen request-logout active desktop

5 Interaction with my PC (2) ctrl-alt-del bad user-passwd logged off login screen confirm-logout crash good user-passwd logout screen change-mind active desktop do-work request-logout

6 UML Statechart Diagram Notation State1 do/action event/action entry/action exit/action Event1(attr) [condition]/action Event trigger With parameters Also: internal transitions Guard condition State2 UML notation based on statecharts by Harel in 1987 Added are a few object-oriented modifications A UML statechart diagram (or UML state machine) can be mapped into a finite state machine (FSM)

7 Statechart Diagrams Graphs whose nodes are states and whose directed arcs are transitions labelled by events. States capture conditions which hold for a period of time e.g. light is on, light is off Events change the state (except internal) e.g. turning the light on, turning the light off Statechart diagrams represent behaviour from the perspective of a single object only An object model with a set of objects must be represented by a set of state diagrams

8 State An abstraction of the attributes of a class State is the aggregation of several attributes of a class Basically an equivalence class of all those attribute values and links that do not need to be distinguished as far as the control structure of the system is concerned Example: State of a user interface screen logged in, logged out, active, idle active is an abstraction of all the user s logged in activity State has duration

9 Event Something that happens at a point in time (e.g. button press, mouse click) Triggers a transition Internal transition (no state change) External transition (change to different state) May result in an action being executed

10 Example 2: vending machine Idle coins_in(amount) / set balance cancel / refund coins Collect Money coins_in(amount) / add to balance [item empty] [select(item)] [change<0] do: test item and compute change [change=0] [change>0] do: dispense item do: make change

11 Another example incidentdocumented incidenthandled incidentarchived States of the Incident object of FRIEND

12 Exercise Draw a state diagram for the book class: A book can be borrowed from the library on a short term or long term loan and then must be returned. A long term loan can only be taken if there is no one on the waiting list. A short term loan can be extended to a long term loan

13 Problem Statement: Direction Control for a Toy Car Power is turned on Car moves forward and car headlight shines Power is turned off Car stops and headlight goes out. Power is turned on Headlight shines Power is turned off Headlight goes out. Power is turned on Car runs backward with its headlight shining. Power is turned off Car stops and headlight goes out. Power is turned on Headlight shines Power is turned off Headlight goes out. Power is turned on Car runs forward with its headlight shining.

14 Headlight off Off on Toy Car: Dynamic Model Wheel Stationary off on Forward off Stationary on On Stationary Stationary on off Stationary off Backward on Stationary

15 Practical Tips for Dynamic Modeling Construct dynamic models only for classes with significant dynamic behavior Avoid analysis paralysis Consider only relevant attributes Use abstraction if necessary Look at the granularity of the application when deciding on actions and activities Reduce notational clutter

16 Exercise Consider the operation of the CITS4401 discussion page: Model the dynamic behavior of a controller object for someone reading and posting to the forum.