University of Toronto at Scarborough © Kersti Wain-Bantin CSCC40 state charts 1 object states an...

University of Toronto at Scarborough © Kersti Wain-Bantin CSCC40 state charts 1

object states

an object state is a condition or situation during the life of an object during which it:

• satisfies some condition• or performs some activity• or waits for some event

the current state of an object determines how it will behave

the current state of an object is determined by:• current values of attributes• and current links with other objects


an object moves from one state to another by a transitionwhich is either:

• triggered by an event • or the state simply finishes (triggerless transition)

statechart diagram is a model of:• all the states and object can have• the events that cause transitions• all possible responses to all use cases

Not all messages an object can receive will alter its state,in particular messages that do not cause changes to attributes or links(e.g. “get” and “query”)


events may trigger action by actor or object

time end of designated time periodafter [time expression]

change when a condition becomes truewhen [Boolean expression]

signal receipt of an asynchronous communication signal

call receipt of call for an operation (synchronous)from self or other object

events

event-signature [guard-condition] / return-value:= action-expression



event-signature operation (parameter-list)guard-condition Boolean expressionaction expression operation (paramter-list)

an example showing multiple actions. . .leftMouseDown(location) [validItemSelected] / menuChoice:= pickMenuItem(location); menuChoiceHighlight ( )

three more examples . . .• /assignManager ( ) ; assignStaff ( )• authorization (authorizationCode) [contract signed] / setCampaignActive ( )• paymentReceived ( payment) [paymentDue – payment <= zero] /

A[B]/Cif told to do A and B is true, then also do C, causing a state changeif told to do A and B is false, then don’t do C and state does not changeif no guard condition, then state always changes


state name

event [guard condition] /action expression

menu visible

itemSelected ( ) / highlightItem ( )entry / displayMenu ( )exit / hideMenu ( )do / playSoundClip ( )

event [guard condition] / action expression

labels and notation



initial state

when [discountStartDate <=currentDate]

when [discountFinishDate <=currentDate]

after [1 year]

discountRate( ) pending

active

lapsed

on creation, theobject moves

immediately into thefirst named state

the event that createsthe object

cannot leave finalstate once it has been

entered

change events

elapsed-time event

transition

basic notation


when [discountStartDate <=currentDate]

when [discountFinishDate <=currentDate]

after [1 year]

discountRate( ) pending

active

lapsed

<<entity>>discountRate

ratediscountStartDatediscountFinishDate

createDiscountRate ( )assignLatestDiscountRate ( )

statechart for the class DiscountRate

createDiscount-Rate ( )


enters hospital

checks in

[diagnosis = healthy]

entering

admitted

released

underobservation

[diagnosis = unhealthy]

[> 2 weeks]

[diagnosis = healthy]

hospital patient


order is created

customersubmits order

order sent for creditauthorization

pending

ordered

credit check denied

customer withdrawsorder request

[authorization= approved]

[authorization= denied]

receivedshippedplacedorder

sent tocustomer

customeraccepts

shipmentorder is closed

online order


reserve (medium type) / update number reserved

available

movie title

<<PK>> movieCode : StringmovieTitle : Stringdirector : StringinStock : Boolean

in stock

reserved

not in stock

ordered

not reserved

[no more reserved]

order item (quantity) [insufficient stock]

replenish stock (quantity)

return item (quantity / add quantity (no items)

rent out (quantity) / subtract item (last item)

put on shelf(quantity)

order item(quantity)

video store – movie title


cancelled ready to ship

filled

stock available[ship date now][canceled]

[canceled]

ship [accepted]

new order

future order

back orderstock not available

stock available [ship date in future]

stock available [ship date in future]

pending

online order


initializing

command

modeling the lifetime of an object

idle

active

entry / setAlarmexit / clearAlarm

checking

waiting

callingentry/callCenter ( )

after (10 seconds) /selfTest

alarm ()

clearattention

attention

alarm system


idle

transmitting

sendFax

ringingreceiving

entry /pickUpexit / disconnect

error / printReport

hangUp

connected

cleaning up

processing

headerOK

checkSumOK

example of nested states within a composite state and triggerless transitions

fax machine


name of state

name of substate 1

name of substate 2

concurrent substates

in this example,either transition T1 or T2can cause the object to leave any of states A1, A2, A3 or B1, B2, B3

and until either T1 or T2occurs, the object remainsin substate 1 and substate 2

A1 A2

A3

B1 B2

B3

T1 T2


when developing state charts . . .

what are the major system events?

what objects are affected by these events?(state charts are created)

what alternate scenarios exist?(state charts are enhanced)

are the state charts consistent with all use cases,collaboration and sequence diagrams?

(state charts are corrected if necessary)


when checking statecharts . . .

every event appears as an incoming message for the appropriate object in the right interaction (sequence or collaboration) diagram? corresponds to an operation on the appropriate class?

every action appears as an operation in that object’s class?

every outgoing message corresponds to an operation in another class?


Menu Visible

itemSelected() / highlightItem() entry / displayMenu exit / hideMenu do / playSoundClip

example: Menu Visible state for a DropDownMenu object

Entry action causes the menu to be displayed

Event itemSelected() triggers the action

highlightItem()

Exiting the state triggers

hideMenu()While the object remains in the Menu Visible state, the activity causes a sound clip

to be played


Synchronized Concurrent Threads.

Synchronization bar

Explicitly showing how an event triggering a transition to a state with nested concurrent states causes specific concurrent substates to be entered

Shows that the composite state is not exited until both concurrent nested statecharts are exited

University of Toronto at Scarborough © Kersti Wain-Bantin CSCC40 state charts 1 object states an...

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