Lab 02 - Interface,Wrapper Class, Exercise 1,2

Exercise 1

General Steps for Modelling with OO Paradigm

1. Identify the nouns (these tell what classes you need).

2. Set up the relationship between the classes. (composition or inheritance or unrelated)

3. Identify the properties and/or data needed to accurately describe the objects identified in Step 1.

4. Identify the functionalities and bahaviour of each class, i.e. what does this class do? (these tell you the methods for each class)

How to determine the fields and methods a class should have?

Single Responsibility Principle

The principles states that:

Each class should only be responsible for doing one single thing.

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Some Tips

1. ID should be described as String, since it is safer.

2. Setters and getters should be used only as a last resort!

3. fluent syntax (when you write your methods, it looks like you are talking to someone). An example is a String Builder class in Java.

Polymorphism

All the subclasses share the same functionality, but the specific outcome of running this functionality varies based on their own implementations.

Use affix to name the subclass. In this Exercise, we can name Arrival to ArrivalEvent.

The use of the parent class, in this example, the Event class, is that:

1. To allow all subclasses to be recognised as Events.

2. To define a set of common properties / behaviors shared across all subclasses.

Thus, one key observation we can find here is that: there's never a need to create an instance of Event!

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Here, it comes the idea of abstract class, which is a class that cannot be instantiated!

And abstract method means that: instances of this abstract class possess a certain behavior, but how exactly this behavior works depends on the subclasses' implementation.

Interface

Models one simple functionality that will be used by different classes.