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Message Types

There are different types
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Synchronous

These are call events
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Guidelines

  • Don't model return value when the value is obvious. e.g. getTotal()
  • Only model return value when it is supposed to be used else where. e.g. as a parameter value for another message
  • Prefer modeling return values as a part of method invocation. e.g. ok = isValid()

Asynchronous

These are signals.
They don't block the caller and are used in multi-threading applications.
Following are the actions they perform: - Create a new thread - Create a new object - Communicate with a thread that is already running

Create

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Destroy

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An object can also destroy itself.

Sequence Diagrams and Logical Complexity

If the diagram is small and simple then it is good.
Otherwise if it is big and complex then it should be broken down into multiple diagrams.

Collaborating Diagrams

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The numbering represents the sequence of event.

Comparing Collaboration and Sequence Diagrams

sequence diagrams are good to see the flow of time.
collaboration diagrams are good to see static object connections.
what is better for understanding sequence of event? sequence diagrams.
what is better for organization and control flow? collaboration diagrams.

Evaluating the Quality of an Object-Oriented Design

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The room in the diagram is not encapsulated as one object.
The heat flow regular has to communicate to different objects, hence increasing the coupling.

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This diagram represents the room as a single object and the coupling is also reduced since the communication is done with one object.

There still exists a problem.
The control is still centralized. We have to make queries to the room object and based on the responses, then we do something about the furnace.

This can be improved by giving the control to the room object itself.
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For example:
a class with a lot of interfaces is more complex to understand.
Instead of doing:

```cpp void SetMinimumValue(int aValue); void SetMaximimumValue(int aValue); 

We can do

```cpp
void SetLimits(int minValue, int maxValue);