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If you’ve ever worked in the field of software engineering, you’ve probably encountered design patterns. Especially in the last 20 years, design patterns have come into popular use as a way of addressing different types of software design issues. While not all engineers will employ design patterns in their everyday work, it’s nonetheless important for engineers to understand their utility.

Read on for our list of ten common design patterns interview questions and answers.

1. Can you explain what a software design pattern is?

A software design pattern is a template that can be used to address problematic issues within different types of software design. Design patterns allow software engineers to address and correct a specific type of software design flaw with a common solution.

2. Can you name a few different types of design patterns?

There are three general classifications of software design patterns which are behavioral patterns, structural patterns, and creational patterns.

3. How would you distinguish a static class from a singleton class?

Unlike singleton classes, a static class is never a top level class and is never compatible with interface implementation. Another difference is the fact that static classes rely on stack memory whereas singleton classes make use of heap memory.

4. Can you list a few types of design patterns you might find in the JDK library?

Design patterns in the JDK library include patterns like singleton pattern, factory pattern, and observer pattern.

5. What is the difference between a design pattern and a framework?

While there are fundamental differences between design patterns and frameworks, it’s actually sometimes difficult to describe the difference between the two because they serve entirely different purposes despite both providing generalized fixes for engineering problems. Essentially, a design pattern’s scope is more limited than that of a framework because a framework offers engineers applicable code whereas a design pattern is more of a guideline or generalized approach to a system issue.

6. What is the general purpose of a design pattern in a workflow?

Design patterns help software engineers efficiently troubleshoot issues with software design in a way that saves time through proven fixes. While design patterns don’t offer specific instructions for fixing software design flaws, they offer software engineers proven frameworks for fixing and approaching a general type of engineer problem.

7. Why is it important to use the right type of design pattern for each specific context?

It’s very important to address engineering flaws with the appropriate type of design patterns. If an engineer uses the wrong type of design pattern to apply a fix s/he might find that an inappropriate fix or alteration has been applied to an entire design, which can present systematic error in complex systems. Perhaps the greatest danger in using design patterns inappropriately occurs when an engineer doesn’t realize the potential effects that a universal change can have. If nothing else, it’s important for engineers to remember that software development includes incredibly complex patterns and design patterns are not always the simple fixes they are made out to be.

8. Who or what is the Gang of Four (GoF)?

The Gang of Four are the four primary innovators of design pattern use. The GoF published the primary text on design patterns, which is called Design Patterns – Elements of Reusable Object-Oriented Software, in 1994. It is thanks to the GoF that design patterns are so widely in use to this day.

9. How many patterns are listed in GoF?

The GoF, which refers specifically to the authors of Design Patterns but is sometimes also used to describe the text itself, contains 23 distinct design patterns.

10. What is a situation in which you would employ a factory pattern to fix a software issue?

Factory patterns are used when a class encounters an issue with creating a specific type of object class. This type of pattern is best used when an engineer must create an object from a particular sub-class.