Object-oriented design has always been a critical part of the software engineering interview process. Most of the engineers struggle with the object-oriented design interviews (OODI), partly because of their lack of experience in laying down the design of a complex system, and partly because of the unstructured nature of OODI. Even engineers, who have some sort of experience in building such systems are not comfortable with these interviews. It is mainly because of the open-ended nature of the design problems that don't have a standard answer.
Here are some of the topics that I had selected from the educational material Grokking the Object-Oriented Design Interview that are deemed useful for your future design interviews.