1

State Diagram

2

State Diagram

State diagram: Shows the behavior of one object. They describe all of the possible states that a particular object can get into and how the object's state changes as a result of events that reach the object.

Other names: State transition diagram Harel diagram (statecharts)

3

Events, States and Transactions

Event: is a significant or noteworthy occurrence. Ex: a telephone receiver is taken off the hook.

State: is a condition of an object at a moment in time (the time between events) Ex: a telephone is in state of being idle after the receiver is placed

on the hook and until it is taken off the hook.

Transaction: is a relationship between two states that indicates that when an event occurs, the object moves from the prior state to the subsequent state. Ex: When the event "off hook" occurs, transition the telephone from

the "idle" to "active" state.

4

5

State Diagram Syntax

Initial and final states: Initial state denoted by a filled black circle and may

be labeled with a name. Final state denoted by a circle with a dot inside, and

may also be labeled with a name.

6

State Diagram Syntax

State Action If the target state had many transitions arriving at it,

and each transition had the same effect associated with it, it would be better to associate the effect with the target state rather than the transitions.

7

State Diagram Syntax

Self Transitions: A state can have transition that return to itself.

8

State Diagram Syntax

Compound state A state diagram may

include sub diagrams.

9

State Diagram Syntax

Entry point When you won’t want to enter a sub-state at the

normal initial state.

10

State Diagram Syntax

Exit point:

11

State Diagram Syntax

Choice Pseudo-State Shown as a diamond with one transition arriving and

two or more transitions leaving.

12

State Diagram Syntax

Junction Pseudo-State used to chain together multiple transitions. A single

junction can have one or more incoming, and one or more outgoing, transitions.

13

State Diagram Syntax

Terminate Pseudo-State The lifeline of the state machine has ended.

14

Example

15

Example

16

Example