Statechart Diagrams

Creating a Statechart Diagram A Statechart diagram shows the life cycle of a single object, from the time that it is created until it is destroyed. These diagrams are a good way to model the dynamic behavior of a class. –1. Right−click the desired class in the browser. –2. Select New / Statechart Diagram from the pop−up menu.

Adding States A state is one of the possible conditions in which an object may exist. –1. Select State from the toolbox toolbar. –2. Click on the Statechart diagram where the state should appear. OR –Select Tools/ Create / State. –Click on the Statechart diagram where the state should appear.

To add documentation to a state: 1.Double−click the desired state to open the state specification window. 2.Select the General tab. 3.Enter documentation in the Documentation field.

Adding State Details There are five types of information you can include for a state: an activity, an entry action, an exit action, an event, or a state history.

Activity

Entry Action An entry action is a behavior that occurs while the object is transitioning into the state.

Exit Action An exit action is similar to an entry action. However, an exit action occurs as part of the transition out of a state.

Activity The behavior in an activity, entry action, or exit action can include sending an event to some other object. For example, if the flight is delayed for more than four hours, the flight object may need to send an event to a flight scheduler object, which will automatically reschedule the flight for another day. In this case, the activity, entry action, or exit action is preceded by a caret (^). The diagram would then read:

Activity

To add an activity: 1.Open the specification window for the desired state. 2.Select the Action tab. 3.Right−click the Actions box. 4.Select Insert from the pop−up menu. 5.Double−click the new action. 6.Enter the action in the Actions field. 7.In the When box, select Do to make the new action an activity.

To add an entry action: 1.Open the specification window for the desired state. 2.Select the Action tab. 3.Right−click the Actions box. 4.Select Insert from the pop−up menu. 5.Double−click the new action. 6.Enter the action in the Actions field. 7.In the When box, select On Entry.

To add an exit action: 1.Open the specification window for the desired state. 2.Select the Action tab. 3.Right−click on the Actions box. 4.Select Insert from the pop−up menu. 5.Double−click the new action. 6.Enter the action in the Actions field. 7.In the When box, select On Exit.

To add an action that occurs on a specific event: 1.Open the specification window for the desired state. 2.Select the Action tab. 3.Right−click the Actions box. 4.Select Insert from the pop−up menu. 5.Double−click the new action. 6.Enter the action in the Actions field. 7.In the When box, select On Event. 8.Enter the event that triggers the action, along with any arguments of the event and any guard conditions that control whether or not the action should occur. If the guard condition is true, the action will occur on the event. If not, the action will not occur, even if the event happens.

To send an event: 1.Open the specification window for the desired state. 2.Select the Detail tab. 3.Right−click the Actions box. 4.Select Insert from the pop−up menu. 5.Double−click the new action. 6.Select Send Event as the type. 7.Enter the event, arguments, and target in their respective fields

Adding Transitions 1.Select Transition from the toolbox toolbar. 2.Click on the state where the transition begins. 3.Drag the transition line to the state where the transition ends.

To add a reflexive transition 1.Select Transition to Self from the toolbox toolbar. 2.Click on the state where the reflexive transition occurs.

To add documentation to a transition: 1.Double−click the desired transition to open the specification window. 2.Select the General tab. 3.Enter documentation in the Documentation field.

Adding Transition Details There are various specifications you can include for each transition. These include events, arguments, guard conditions, actions, and send events.

Event An event is something that causes a transition from one state to another to occur. On the diagram, an event can be drawn using an operation name or simply using an English phrase Events can have arguments. For example, when removing a passenger, we will need the name of the passenger to be removed.

Guard Condition A guard condition controls when a transition can or cannot occur. In the airline example, adding a passenger will move the flight from the Open to the Full state, but only if the last seat was sold. The guard condition in this example is "Last seat was sold.“ A guard condition is drawn along the transition line, after the event name, and enclosed in square brackets.

Action An action, as we mentioned above, is a noninterruptible behavior that occurs as part of a transition. Entry and exit actions are shown inside states, because they define what happens every time an object enters or leaves a state. For example, when transitioning from the Scheduled state to the Open state, we may want to initialize the number of passengers at 0. An action is shown along the transition line, after the event name, and preceded by a slash.

Adding Transition Details An event or action may be a behavior that occurs inside the object or a message that is sent to another object. If an event or action is sent to another object, it is preceded by a caret (^) on the diagram.

To add an event: 1.Double−click the desired transition to open the specification window. 2.Select the General tab. 3. Enter the event in the Event field.

To add arguments to an event: 1.Double−click the desired transition to open the specification window. 2.Select the General tab. 3.Enter the arguments in the Arguments field.

To add a guard condition: 1.Double−click the desired transition to open the specification window. 2. Select the Detail tab. 3. Enter the guard condition in the Condition field.

To add an action: 1.Double−click the desired transition to open the specification window. 2. Select the Detail tab. 3. Enter the action in the Action field.

To send an event: 1.Double−click the desired transition to open the specification window. 2. Select the Detail tab. 3.Enter the event in the Send Event field. 4. Enter any arguments in the Send Arguments field. 5. Enter the target in the Send Target field.

Create a Statechart Diagram Create the Statechart diagram shown in

Exercise Steps: Create the Diagram –1.Locate the Product class in the browser. –2. Right−click the class and select New Statechart Diagram.

Exercise Steps Add the Start and Stop States 1.Select Start State from the toolbox. 2.Place the state on the diagram. 3.Select End State from the toolbox. 4.Place the state on the diagram.

Add the States 1. Select State from the toolbox. 2. Place the state on the diagram. 3. Name the state Ordered. 4. Select State from the toolbox. 5. Place the state on the diagram. 6.Name the state Inventoried.

Add the States 7.Select State from the toolbox. 8.Name the state Out of Stock. 9.Select State from the toolbox. 10.Name the state Selected for Purchase. 11. Select State from the toolbox. 12.Place the state on the diagram. 13.Name the state Purchased.

Add Transitions 1. Select Transition from the toolbox. 2. Click the Start State. 3. Drag the transition line to the Ordered state.

4. Repeat steps 1–3 to add the following transitions: –Ordered to Out of Stock –Ordered to Inventoried –Inventoried to Selected for Purchase –Selected for Purchase to Inventoried –Selected for Purchase to Purchased –Purchased to End State –Out of Stock to End State –Inventoried to End State

Add Transition Details 1.Double−click the Ordered to Out of Stock transition to open the specification. 2.Select the Detail tab. 3.In the Guard Condition field, enter backordered. 4. Click OK to close the specification.

Add Transition Details 5. Repeat steps 1–4 to add the guard conditions to the following transitions: