How to Approach OOP Questions

Handle Ambiguity

• When being asked an object-oriented design question,
  • you should inquire _who _ is going to use it and _how _ they are going to use it.
• Depending on the question, you may even want to go through the "six _Ws":
  • _ who, what, where, when, how, why.

Define the Core Objects

• Now that we understand what we're designing, we should consider what the “core objects” in a system are.

• For example,
  • suppose we are asked to do the object-oriented design for a restaurant. Our core objects might be things like Table, Guest, Party, Order, Meal, Employee, Server, and Host.

class Guest{

}

class Party{

}

class Meal{

}
...

Analyze Relationships

• Having more or less decided on our core objects, we now want to analyze the relationships between the objects.
• Which objects are members of which other objects? Do any objects inherit from any others? Are relationships many-to-many or one-to-many?

• For example, in the restaurant question, we may come up with the following design:
  • the Party should have an array of Guests.
  • Server and Host inherit from Employee.
  • Each table has one party, but each Party may have multiple Tables .
  • There is one Host for the Restaurant.

class Party{
	Guests[] guests;
}

class Server extends Employee{

}
...

Investigate Actions

• At this point, you should have the basic outline of your object-oriented design. What remains is to consider the key actions that the objects will take and how they relate to each other.
• You may find that you have forgotten some objects, and you will need to update your design.
• Example:
  • Action of Guests include
    • makeOrder()
    • pay()
    • changeTable()
    • callServer()

class Guest{

	public void makeOrder(){
	}
	
	public void pay(){
	
	}
	...
}
...