Topic 3
Topic 3 has 3 parts: Collaboration, Memory, and UML Sequence Diagrams
Topic 03 - Part A - Collaboration
OOP uses objects that interact with eachother. Object relationships are the backbone of Object Oriented Programs.
There are three main kinds of relationships:
1. Association
Association is used for "has" relationships. Such as "Ben has a Website".
2. Aggregation
Aggregation is used when an object is part of something else. Such as "Object Oriented Programming is part of Computer Science" or "Reverse Card is part of the Uno Deck"
3. Dependence
Dependence is very self-explanatory. It is when an object depends on another one. For example "This website uses HTML" or "Soccer uses Soccer Ball".
These are mainly used for temporary "use" relationships, hence the terminology.
Topic 03 - Part B - Memory
This part is all about stacks/heaps.
Pointers and references allow objects to be flexibly networked.
When the project runs (runtime), all objects exist in the heap.
Different languages use a "pointer" in order to reference objects.
| C# and Java | C++ and Objective C |
|---|---|
| Reference types Value types | Pointers Types |
Pointers make the flexible relationships happen.
An object is "aware" of other objects, and can request that the other object does something.
Topic 03 - Part C - UML Sequence Diagrams
Another aspect of the UML diagrams the sequence diagrams.
UML sequence diagrams showcase a sequence of communication between different objects. A "message" is sent out and changes over time. They are relatively intuitive to read/understand. A sample of one can be seen below.
Photo credit: Microsoft Visio Docs