What have I learned about the term “Association”?

For in-class activities of this week, we learned about modeling with UML class diagram. There were many important elements to compose a class, such as properties, operations, and association. However, my team got stuck at the “association” section, we could not clearly distinguish the different types of relationships between two classes, especially the relationship named have-a. Therefore, I thought it was a good opportunity for myself to learn more about the term “association”.

There are many articles and blogs analyzing about different types of relationships between classes. However, many of them look very complicated with a long list of different relationship types and some are very confusing. Fortunately, I found this article, entitled Association, Composition and Aggregation in Java, which finally satisfied my curiosity about “association”, because the content of this article is focused only into the definition of “association” and the analysis of its types which are aggregation and composition.

There are some key points that I have taken away after reading the article. First, association represents a relationship between two classes, depending on each situation, association can be one-to-one, one-to-many, many-to-one, and many-to-many. Second, association has two special forms, which are aggregation and composition.

For aggregation, this term is also known as has-a relationship (a weak association), which is one way relationship and each entity of the relationship can exist independently. The author also provides a simple example to describe those characteristics of aggregation, which is an Institute has-a Department, and Department has-a Student. This is one way relationship because a department can have students, but vice versa is impossible. Moreover, if the Department class is removed, the Student class can still exist independently.

For composition, this is the part-of relationship (a strong association), and the two entities are dependent to each other, which means a class (child) cannot exist without the existing of another class (parent). For this definition, the author gives an example of Book and Library, Book is part-of Library. So, if Library class is removed, Book class cannot exist. In my opinion, this example does not make sense to the part-of relationship because I think Book still can exist without Library. Therefore, I have looked for other resources to find a good example for composition. UML Association vs Aggregation vs Composition is a good resource to provide real-life examples for each conception. Like the first article, this one also focuses on the analysis of the term “association” and its two special types, aggregation and composition. According to the article, I got an example that Head, Hand, Leg are part-of Person. Thus, if Person class is removed, Head, Hand and Leg classes cannot exist. For myself, this is a perfect example to describe the term composition.

In short, I have learned a lot of information and had a clear understanding about the term “association” from the two articles recommended above. I will apply this knowledge to design relationships between classes in my UML diagrams. Moreover, I believe the articles that I choose are good resources because their content is clearly organized with good examples. In other words, I would say the two articles complement each other, so it is good if readers can pull out the best parts from each article and be able to combine them consistently.

Polymorphism

This week, we reviewed about the concepts and the differences between the five terms, which were abstraction, interface, inheritance, encapsulation, and polymorphism. However, the term polymorphism confused me a lot during the class. The only thing that I remembered about polymorphism was that a class or an object could exist in many forms, but I could not explain to myself what “forms” mean. So, I did some searching on the term polymorphism in the hope that I could recall what I had learned and also learn more about the characteristics of polymorphism.

Fortunately, I found a good resource, called Polymorphism, Encapsulation, Data Abstraction, and Inheritance in Object Oriented Programming, written by Nick. Through this blog, Nick provides readers with concise definitions of abstraction, encapsulation, inheritance, and polymorphism with typical properties respect to each term. The writer also analyzes the important role of each concept in programming. Furthermore, after defining each term, Nick also has at least one example to describe the definition making the terms easier to understand for code newbies. This is one of the reasons that I chose this blog as my resource. In particular, in the polymorphism section, Nick gives an example of the class “Move” and the classes of animals to explain the phrase “exists in many forms”. The class “Move” does not have a concrete type, so it can be inherited/extended by any type of animal. For example, a Snail will crawl to move, a fish will swim to move, or a Kangaroo will leap to move. Hence, the concept of polymorphism is applied to make the code more flexible and extensible. This is a good blog to read and very useful if you want to understand clearly about the concepts of polymorphism, encapsulation, abstraction, and inheritance. I might forget these concepts if I don’t use them for a while. However, this blog gives me a key to remember those concepts in the long run by keeping in mind the real life examples provided by the blog.

Another thing is that after reading the blog, I know that there are several different types of polymorphism, but the writer does not analyze those types in depth in the blog. Therefore, I searched other sources to learn more about polymorphism. Different resources give me different numbers of polymorphism types. However, there is an article, called Polymorphism in Java, that gives me the necessary information about the types of polymorphism. There are many types of polymorphism, but in Java language, there are only two, which are compile-time polymorphism (overloading) and runtime polymorphism (overriding). Throughout the article, each type is described and analyzed using code examples. For myself, this is a good resource because although the article is short but concise, it contains all the information I need to know. Moreover, before reading the article, I had a chance to learn about the concepts of overloading and overriding, but I did not know how those two methods relate to the concept of polymorphism. So, the article not only helped me review my old knowledge, but also helped me to come up with the idea that I would organize all the concepts that I have learned into a diagram, where the diagram will show how concepts relate to each other. I believe the diagram will be one of my best tools that I can use to remember and distinguish all the important concepts in programming.

CS-343 Introduction.

Hello!

My name is T (Hien Chau). I am a junior and double majoring in Computer Science and Mathematics at Worcester State University. I will use this blog to record and to share what I have learned, discovered or experienced during this CS-343 course. It is really nice to meet all of you in person instead of meeting on Zoom. I hope everyone has a great semester!

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