Top 250 Design Patterns Interview Questions and Answers

Create an Observer class

• Observer class is used to notify changes to multiple objects

• It maintains a list of objects that need to be notified

• It has methods to add, remove and notify observers

• Example: Weather station notifying multiple displays

I implemented the API Gateway pattern to break the monolith into microservices.

• API Gateway pattern acts as a single entry point for clients to access multiple microservices.

• It helps in decoupling the client from individual microservices.

• API Gateway h...read more

Factory pattern is used to create objects without exposing the instantiation logic to the client, while Singleton pattern ensures a class has only one instance and provides a global point of access to it.

• Factory pattern is used to create objects base...read more

Obser is not a known term in software engineering.

• Obser is not a known term in software engineering.

• It is possible that the interviewer misspoke or meant to ask a different question.

• It is important to clarify any unclear or confusing questions during...read more

The class used in Factory method is the Factory class.

• The Factory class is responsible for creating objects of different classes based on the input parameters.

• It is a creational design pattern.

• The Factory method is a static method that returns an obj...read more

Visitor pattern is a design pattern where a visitor class is used to perform operations on elements of a data structure.

• Visitor pattern allows adding new operations to existing classes without modifying them

• It separates the algorithm from the object ...read more

Java design patterns are reusable solutions to common problems encountered in software design.

• Java design patterns help in creating flexible, reusable, and maintainable code.

• Examples of Java design patterns include Singleton, Factory, Observer, and S...read more

Design patterns in SQL are reusable solutions to common problems encountered in database design and development.

• Singleton Pattern: Ensures a class has only one instance and provides a global point of access to it.

• Factory Pattern: Creates objects with...read more

An analytical framework for IPL bidding system

• Identify key performance indicators (KPIs) such as player performance, team performance, market value, etc.

• Collect and analyze historical data on player and team performance, auction prices, and market tr...read more

The design pattern commonly used in Angular is the Observer pattern.

• The Observer pattern is used to establish a one-to-many dependency between objects.

• In Angular, Observables are used to implement the Observer pattern for handling asynchronous data s...read more

Factory pattern is a creational design pattern that provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.

• Create an interface or abstract class to define the factory method...read more

Design patterns are reusable solutions to common software design problems.

• Design patterns provide a common language for developers to communicate about software design.

• They can improve code quality, maintainability, and scalability.

• Examples of design...read more

Design patterns are reusable solutions to common problems in software design, while design principles are guidelines to follow for good design practices.

• Design patterns provide specific solutions to recurring problems in software design, such as Sing...read more

Decorator pattern adds behavior to an object dynamically without affecting its existing behavior.

• It is a structural pattern

• It involves a component interface, concrete component, decorator interface, and concrete decorator

• Decorators wrap around compon...read more

Factory creates objects without specifying the exact class, while builder constructs complex objects step by step.

• Factory pattern creates objects without specifying the exact class to create, using a common interface.

• Builder pattern constructs comple...read more

Object-oriented concepts and design involve creating classes and objects that encapsulate data and behavior.

• Object-oriented programming is based on the principles of encapsulation, inheritance, and polymorphism.

• Classes are used to define objects, whi...read more

A fail-safe iterator should handle exceptions and errors gracefully without crashing the program.

• Use try-catch blocks to handle exceptions and errors

• Implement a hasNext() method to check if there are more elements to iterate over

• Use a current pointer...read more

Design a library to log drop-rate in form fields.

• Create a function to track changes in form fields

• Implement a mechanism to calculate drop-rate based on user interactions

• Store drop-rate data in a database for analysis

A mood 3 counter is a device that tracks and displays the user's mood on a scale of 1-3.

• Design a simple interface with 3 buttons for the user to input their mood (happy, neutral, sad)

• Include a display screen to show the current mood level

• Implement a ...read more

Relays in Dependency Injection are used to control the creation and lifecycle of objects.

• Relays help in decoupling the creation of objects from their usage.

• They can be used to provide different implementations of an interface based on certain conditi...read more

Design patterns in Unity are reusable solutions to common problems in game development.

• Design patterns help in organizing code, improving code readability, and promoting code reusability.

• Examples of design patterns in Unity include Singleton, Observe...read more

Use synchronized block or double-checked locking to ensure only one thread can access singleton instance at a time.

• Use synchronized block to ensure thread safety in getInstance() method

• Implement double-checked locking to minimize synchronization over...read more

Singleton design pattern ensures a class has only one instance and provides a global point of access to it.

• Ensure a class has only one instance by providing a global access point to it

• Lazy initialization to create the instance only when needed

• Thread-...read more

To design a 2 model in single window, use a split screen or tabbed interface.

• Consider the user's workflow and prioritize the most important information

• Use a clear visual hierarchy to differentiate between the two models

• Provide easy navigation between...read more

ViewModel is a class that is responsible for preparing and managing data for an activity or fragment.

• ViewModel helps in separating the UI data from the UI controller logic.

• It survives configuration changes such as screen rotations.

• ViewModel is part o...read more

Yes, I have created custom facades to provide a simplified interface to a complex subsystem.

• Used to improve code readability and maintainability

• Helps in decoupling the client code from the subsystem

• Examples: Laravel's Facade pattern for database oper...read more

Circuit breaker pattern is a design pattern used to prevent cascading failures in distributed systems.

• It is used to handle faults that may occur in a distributed system

• It monitors the availability of a service and trips when the service fails

• It preve...read more