OOD Design

Step 1：

Who is going to use it. How they are going to use it.

Or： Who, What, Where, When, how, Why

Step 2: 

Define Core Objects.

　　Example:

• 　　Resaturant:

　　　　Table, Guest, Party(Order), Order, WaitLine, Reservation, Meal, Employee, Server and Chef.

• 　　Chess：

　　　　Table, Player, Piece

Step 3：

Analyze Relationship

• Many to Many
• One to Many 

Talk to interviewer about how general purpose your design should be.

Example:

　　Resturant:

• One table has one Order, One order can have one or multi tables
• Server and Chef inherits from Employee.
• One table has one or multi Guest
• One wait line will keep the name of one order(party)
• The reserveation array will keep the name of reservation. Dictionary may be better

Step 4:

Inverstigate Actions

update your design

Example:

　　Resturant:

• 　　Main Process

1. Guests come
2. Check Reservation
3. Yes, Go to table
4. No, Check Table empty
5. empty, assign to the table.
6. No empty, add it to the waiting line
7. Guests sit down
8. Assign a server to delivery the menu and beverages
9. Get Order
10. Send Order to chef(Then we need a queue for Order)
11. Order was accept and cooked
12. Delivery the dishes(Then we need dish class with price)
13. Table checked out
14. Server check the money and free the table
15. Judge waiting line is empty or not
16. Not, assign the table
17. Empty, do nothing

• Reservation Process:

1. Guest call and make a reserve
2. Check table empty
3. No, cannot reserve
4. Yes, reserve and make the table reserved(so table can be empty, seated or reserved)

Design Pattern:

Singleton and Factory

Singleton:

Can only be instanced once, such as Chess table or restaurant's restaurant itself. So we may need static keyword.

Factory:

An interface for creating an instance of a class, such as create order.The factory method would take a parameter representing which class to instantiate.

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Some samples:

Chat Server

Design Twitter

Design Hashtable

LRU Cache

Parking Lot

Tic-Tac-Toe

Call center

Some follow up questions：

what would be the hardest problems to solve?