Java Interview Questions – Design Patterns

Q1: [Amazon] What are design patterns in Java?

Answer: Design patterns are standard solutions for common software design problems.

Q2: [Facebook] What is the Singleton pattern?

Answer: The Singleton pattern ensures only one instance of a class exists. Example:

public class Singleton {

    private static Singleton instance;

    private Singleton() { }

    public static Singleton getInstance() {

        if (instance == null) { instance = new Singleton(); }

        return instance;

    }

}

Q3: [Adobe] What is the Factory pattern?

Answer: The Factory pattern provides a method to create objects without specifying their concrete class.

Q4: [Netflix] What is the difference between Strategy and Observer patterns?

Answer:

• Strategy: Used for interchangeable algorithms at runtime.
• Observer: Used for event-driven systems (one-to-many dependency).

Q5: [Uber] What is the Builder pattern in Java?

Answer: The Builder pattern simplifies object creation for complex objects with multiple parameters.