20 Design Patterns and Software Design Interview Questions for Programmers

Here are 20 design patterns and software design interview questions that can be useful for programmers:

Singleton Pattern:

Explain the Singleton design pattern and when you would use it.

What are the advantages and disadvantages of the Singleton pattern?

Observer Pattern:

Describe the Observer design pattern and its purpose.

How is the Observer pattern different from the Pub-Sub pattern?

Factory Pattern:

Explain the Factory design pattern and its benefits.

Compare the Factory pattern with the Abstract Factory pattern.

Adapter Pattern:

What is the Adapter design pattern used for?

Provide an example of how the Adapter pattern can be applied.

Decorator Pattern:

Describe the Decorator design pattern and its usage.

How does the Decorator pattern differ from inheritance?

Strategy Pattern:

Explain the Strategy design pattern and its benefits.

How is the Strategy pattern related to the concept of polymorphism?

Command Pattern:

Describe the Command design pattern and its purpose.

How does the Command pattern support the principle of separation of concerns?

Proxy Pattern:

What is the Proxy design pattern used for?

Provide an example scenario where the Proxy pattern can be applied.

Builder Pattern:

Explain the Builder design pattern and its advantages.

Compare the Builder pattern with the Factory pattern.

Prototype Pattern:

Describe the Prototype design pattern and its usage.

What are the differences between shallow copy and deep copy in the Prototype pattern?

Template Method Pattern:

What is the Template Method design pattern?

How does the Template Method pattern promote code reuse and extensibility?

Iterator Pattern:

Explain the Iterator design pattern and its purpose.

Provide an example of using the Iterator pattern in a real-world scenario.

Composite Pattern:

Describe the Composite design pattern and when it is applicable.

How does the Composite pattern enable treating individual objects and compositions uniformly?

State Pattern:

What is the State design pattern used for?

How does the State pattern differ from using a switch/case statement?

Mediator Pattern:

Explain the Mediator design pattern and its benefits.

Provide an example scenario where the Mediator pattern can be useful.

Flyweight Pattern:

Describe the Flyweight design pattern and its purpose.

How does the Flyweight pattern optimize memory usage?

Chain of Responsibility Pattern:

What is the Chain of Responsibility design pattern?

How does the Chain of Responsibility pattern promote loose coupling?

Visitor Pattern:

Explain the Visitor design pattern and its usage.

How does the Visitor pattern separate algorithms from the objects they operate on?

Memento Pattern:

Describe the Memento design pattern and its purpose.

How can the Memento pattern be used to implement undo/redo functionality?

Dependency Injection Pattern:

What is Dependency Injection (DI) and how does it relate to the Inversion of Control (IoC) principle?

Describe different types of DI and provide an example of using DI in a project.

These questions cover a range of design patterns commonly used in software development and can help assess a candidate's understanding of software design principles and their ability to apply these patterns to real-world scenarios.