sgdev: Interview Question: Design an Object Oriented System

sgdev: Interview Question: Design an Object Oriented System

Data structures and algorithms

It may appear that OO design questions can be answered while avoiding data structures and algorithms. This is not true. An interface or class may need to use an abstract data type or a well known algorithm in its implementation.
As an example assume the OO system to design is a syntax checker. You may define an interface which checks for balanced parentheses. The interviewer may want to know how you would implement the interface.
Even if you don't know the answer off the bat, you could ask the interviewer for a hint or think of a naive answer which might lead to a good solution. The key is to know about the stack abstract data type and its operations. If you don't know anything about stacks, this could become a difficult problem and raise a red flag with the interviewer.

It is good to know how to estimate time and space complexity of algorithms since interviewers may want to know if you can use this knowledge for design trade-offs.

Some ways to improve knowledge of data structures and algorithms:
Books Internet articles
Exercises
Perusing the standard library of your language
Work on projects.

Heuristic

Some approaches to the object oriented job interview question:

1. In my interviews, I wrote down interfaces and base classes which occurred as I described use cases to the interviewers. Then I began writing out the interactions between the objects. I asked questions when I faced ambiguity in my assumptions. This approach allowed me to engage the interviewer in the design process. However I thought it was a vague method when we got into the details and the interviewers started adding and modifying requirements.

2. A more precise way is to write down use cases first. Based on the use cases, come up with the objects. Then use a method like CRC cards to flush out the interactions between the objects. Use a message sequence diagram to refine the interactions. Finally use a deployment diagram to show various processes which host the objects as they run on computers and network elements. While this is a methodical way of doing object oriented design, it may not be the best approach within the constraints of a job interview.

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