Understanding Objects and Object Flows

The object flow sample demonstrates how activities affect object state on activity diagrams. The object flow sample illustrates three important aspects of activity diagram objects:

• Objects may appear more than once and in several states.
• Activities may change object states.
• Objects connect with activities through object flows.

Figure 52 CD Player Sample

In Figure 52 on page 117, notice that the CD Player object appears on the diagram more than once. However, each object appears in a different state: playing, paused, and stopped. Each activity in the sample changes the state of the CD Player when you push the various buttons or perform the activity. For example, when you push the Pause button, the state of the CD Player changes to [Paused].

In most cases, the same object may be (and usually is) the output of one activity and the input of one or more subsequent activities.

Changing the State of an Object

To change the state of an object on an activity diagram:

1 Double-click the object to display the Object Specification.

2 Select New from the State list.

A new State Specification appears.

3 Enter descriptive information about the object state in the State Specification.

4 Click OK to close the State Specification.

5 Click OK to close the Object Specification.

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Shared State Machine Diagram Model Elements

This section describes the elements that can appear in both activity diagrams and statechart diagrams: