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
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 1
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”)
an object moves from one state to another by a transition
which is either:
• triggered by an event
• or the state simply finishes (triggerless transition)
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 2
events
events may trigger action by actor or object
time
end of designated time period
after [time expression]
change
when a condition becomes true
when [Boolean expression]
signal
receipt of an asynchronous communication signal
call
receipt of call for an operation (synchronous)
from self or other object
event-signature [guard-condition] / return-value:= action-expression
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 3
event-signature [guard-condition] / return-value:= action-expression
event-signature
guard-condition
action expression
operation (parameter-list)
Boolean expression
operation (paramter-list)
A[B]/C
if told to do A and B is true, then also do C, causing a state change
if told to do A and B is false, then don’t do C and state does not change
if no guard condition, then state always changes
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] /
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 4
labels and notation
state name
menu visible
event [guard condition] /
action expression
itemSelected ( ) / highlightItem ( )
entry / displayMenu ( )
exit / hideMenu ( )
do / playSoundClip ( )
event [guard condition] / action expression
event-signature [guard-condition] / return-value:= action-expression
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 5
the event that creates
the object
on creation, the
object moves
immediately into the
first named state
initial state
basic notation
discountRate( )
pending
when [discountStartDate <=
currentDate]
change events
active
transition
when [discountFinishDate <=
currentDate]
lapsed
after [1 year]
elapsed-time event
cannot leave final
state once it has been
entered
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 6
statechart for the class DiscountRate
createDiscountdiscountRate( )
Rate ( )
pending
when [discountStartDate <=
currentDate]
active
<<entity>>
when [discountFinishDate <=
currentDate]
discountRate
rate
discountStartDate
discountFinishDate
lapsed
after [1 year]
createDiscountRate ( )
assignLatestDiscountRate ( )
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 7
hospital patient
enters hospital
entering
checks in
admitted
[diagnosis = unhealthy]
under
observation
[diagnosis = healthy]
released
[diagnosis = healthy]
[> 2 weeks]
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 8
order is created
pending
customer withdraws
order request
online order
customer
submits order
ordered
order sent for credit
authorization
credit check
[authorization
= denied]
denied
[authorization
= approved]
placed
University of Toronto at Scarborough
order
sent to
customer
© Kersti Wain-Bantin
shipped
received
customer
accepts
shipment
order is closed
CSCC40 state charts 9
movie title
<<PK>> movieCode : String
movieTitle : String
director : String
inStock : Boolean
available
rent out (quantity) / subtract item (last item)
video store –
movie title
not in stock
return item (quantity / add quantity (no items)
put on shelf
(quantity)
order item
(quantity)
replenish stock (quantity)
in stock
ordered
order item (quantity) [insufficient stock]
[no more reserved]
reserved
reserve (medium type) / update number reserved
University of Toronto at Scarborough
© Kersti Wain-Bantin
not reserved
CSCC40 state charts 10
online order
pending
new order
back order
stock not available
stock available
[ship date in future]
future order
stock available [ship date in future]
stock available
[ship date now]
[canceled]
cancelled
[canceled]
ready to ship
ship [accepted]
filled
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 11
alarm system
after (10 seconds) /
selfTest
alarm ()
active
initializing
idle
attention
checking
calling
entry/callCenter ( )
clear
command
waiting
attention
entry / setAlarm
exit / clearAlarm
modeling the lifetime of an object
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 12
fax machine
ringing
receiving
connected
idle
headerOK
hangUp
processing
sendFax
checkSumOK
cleaning up
transmitting
error
/ printReport
entry /pickUp
exit / disconnect
example of nested states within a composite state
and triggerless transitions
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 13
concurrent
substates
name of state
name of substate 1
A1
A2
A3
in this example,
either transition T1 or T2
can cause the object
to leave any of states
A1, A2, A3 or B1, B2, B3
name of substate 2
B1
B2
and until either T1 or T2
occurs, the object remains
in substate 1 and substate 2
B3
T1
University of Toronto at Scarborough
T2
© Kersti Wain-Bantin
CSCC40 state charts 14
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)
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 15
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?
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 16
example: Menu Visible state
for a DropDownMenu object
Event itemSelected() triggers
the action highlightItem()
Entry action
causes the menu
to be displayed
Menu Visible
itemSelected() / highlightItem()
entry / displayMenu
exit / hideMenu
do / playSoundClip
Exiting the state
triggers hideMenu()
While the object remains in
the Menu Visible state, the
activity causes a sound clip
to be played
University of Toronto at Scarborough
© Kersti Wain-Bantin
CSCC40 state charts 17
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 18