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.

Difference between getPath(), getCanonicalPath() and getAbsolutePath() of File in Java - Example

In Java, the File class provides several methods for working with file paths. Here are the differences between getPath(), getCanonicalPath(), and getAbsolutePath():

 getPath(): 

The getPath() method returns the path of the file or directory as it was specified when the File object was created. It may be a relative path or an absolute path depending on how the File object was instantiated. 

If the file path contains symbolic links or relative path components, getPath() does not resolve them. 

Example:

File file = new File("mydir/example.txt");
String path = file.getPath();
System.out.println(path);

Output:

mydir/example.txt

getCanonicalPath(): The getCanonicalPath() method returns the canonicalized path of the file or directory. 

It resolves the file path by removing any symbolic links, resolving relative paths, and returning the absolute path.

 It returns a standardized path representation without any unnecessary components or redundant separators.

File file = new File("mydir/../mydir/example.txt");
String canonicalPath = file.getCanonicalPath();
System.out.println(canonicalPath);

Output:

/home/user/mydir/example.txt

getAbsolutePath(): The getAbsolutePath() method returns the absolute path of the file or directory. It provides the complete path from the root of the file system. 

If the File object was created with a relative path, getAbsolutePath() resolves it to an absolute path by prepending the current working directory. 

Example:

File file = new File("mydir/example.txt");
String absolutePath = file.getAbsolutePath();
System.out.println(absolutePath);

Output:

/home/user/current-working-directory/mydir/example.txt

It's important to note that all three methods may throw IOException if the file or directory does not exist or if an I/O error occurs during path resolution.

In summary, getPath() returns the path as provided, getCanonicalPath() returns the standardized, resolved path, and getAbsolutePath() returns the absolute path by resolving relative paths against the current working directory.

Difference between jQuery Document Ready Method and JavaScript Window Onload Event

The jQuery document.ready() method and the JavaScript window.onload event are both used to execute code when the HTML document has finished loading. However, there are a few key differences between them:

Execution Time:

jQuery document.ready(): The code inside $(document).ready() is executed as soon as the DOM (Document Object Model) is ready, which means it can run before all the external resources (such as images) have finished loading.

JavaScript window.onload: The code inside the window.onload event is executed only after the entire page, including external resources, has finished loading. It waits for everything, including images, scripts, and stylesheets, to be fully loaded.

Multiple Handlers:

jQuery document.ready(): You can have multiple $(document).ready() handlers in your code, and they will all be executed when the DOM is ready. They will run in the order they were declared.

JavaScript window.onload: Only one window.onload event handler can be assigned at a time. If you assign multiple handlers, the last one assigned will overwrite any previous ones.

Simplicity:

jQuery document.ready(): The $(document).ready() method is part of the jQuery library and provides a simpler syntax for executing code when the DOM is ready. It abstracts away some of the cross-browser compatibility issues that the window.onload event may encounter.

JavaScript window.onload: The window.onload event is a native JavaScript event, and using it directly requires more verbose code compared to the jQuery method. It may also require additional checks for cross-browser compatibility.

In general, if you are already using jQuery in your project, using $(document).ready() is a convenient way to ensure your code runs when the DOM is ready. However, if you're working with plain JavaScript or have specific requirements for waiting until all external resources are loaded, using the window.onload event is a better choice.

Top 3 Courses to Learn Deno in 2023 - Best of Lot

As of my knowledge cutoff in September 2021, Deno is a relatively new JavaScript runtime that provides a secure and modern environment for running JavaScript and TypeScript applications. While I cannot provide real-time information on the courses available in 2023, I can recommend three popular courses for learning Deno that were highly regarded at the time:

"The Deno Course - Beginner to Advanced" by Maximilian Schwarzmüller on Udemy: This comprehensive course covers Deno from the basics to advanced topics. It includes hands-on exercises, practical examples, and covers important concepts such as modules, permissions, testing, and deployment.

"Deno: The Complete Guide" by Academind on Udemy: This course offers a thorough introduction to Deno, covering its features, modules, security model, and more. It also includes practical projects to reinforce your learning and provides insights into the similarities and differences between Deno and Node.js.

"Deno - The Complete Deno.js Developer Course" by Brad Traversy on Udemy: In this course, you'll learn Deno from scratch, including setup, working with modules, understanding TypeScript, building RESTful APIs, and creating a real-time chat application. The course provides practical examples and projects to reinforce your knowledge.

Keep in mind that the availability and quality of courses may change over time, so it's advisable to search for the latest Deno courses on popular e-learning platforms like Udemy, Coursera, or Pluralsight. Additionally, exploring official Deno documentation, tutorials, and community resources can also be helpful in staying up to date with the latest developments in Deno.

Top 5 Websites to Learn Golang in 2023 - Best of Lot

In 2023, there are several excellent websites where you can learn Golang (Go) programming. Here are five top websites that provide high-quality resources and tutorials for learning Golang:

Go by Example (https://gobyexample.com/): Go by Example is an interactive website that offers concise and practical examples of Go code. It covers a wide range of topics, from basic syntax to more advanced concepts, making it an excellent resource for beginners and intermediate learners.

Golang.org (https://golang.org/): The official website of the Go programming language, Golang.org, provides comprehensive documentation, tutorials, and resources for learning Go. It covers everything from the language basics to advanced topics like concurrency and networking. The website also includes a "Tour of Go" section that offers interactive exercises for hands-on learning.

Learn Go with Tests (https://quii.gitbook.io/learn-go-with-tests/): Learn Go with Tests is an online book that teaches Go through a test-driven development (TDD) approach. The book takes you step-by-step through building real-world applications using tests as your guide. It's a practical and engaging way to learn Go while gaining experience with TDD principles.

Go Bootcamp (https://www.golangbootcamp.com/): Go Bootcamp is a comprehensive online course specifically designed to teach Go programming. It covers the language fundamentals, common patterns, and practical examples. The course includes exercises and quizzes to reinforce your understanding of the concepts. It's a paid course, but it offers a wealth of knowledge for those serious about learning Go.

A Tour of Go (https://tour.golang.org/welcome/1): A Tour of Go is an interactive online tutorial provided by Golang.org. It allows you to learn Go through a series of interactive lessons. Each lesson introduces a new concept and provides coding exercises to practice what you've learned. It's an excellent resource for beginners to get hands-on experience with Go.

These websites offer a variety of learning materials, including examples, tutorials, documentation, and interactive exercises. Depending on your preferred learning style, you can choose the resources that best suit your needs. Remember to practice writing code, work on projects, and seek out additional learning resources to deepen your understanding and proficiency in Go programming.