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Q1. What is Object-Oriented Programming (OOP)?

ANS. OOP is a programming paradigm that models real-world entities as objects, each with its own properties and behaviors.

Q2. What are the four pillars of OOP?

• Inheritance: Allows classes to inherit properties and methods from other classes.
• Encapsulation: Hides data within objects and provides controlled access.
• Polymorphism: Enables objects of different classes to be treated as if they were of the same type.
• Abstraction: Defines a blueprint for objects, focusing on essential characteristics.

Q3. Explain the difference between a class and an object.

ANS.  A class is a blueprint for creating objects. An object is an instance of a class.

Q4. What is the constructor and destructor in PHP?

ANS.  A constructor is a special method that is automatically called when an object is created. A destructor is a special method that is automatically called when an object is destroyed.

Q5. What is the purpose of the $this keyword in PHP?

ANS. The $this keyword refers to the current object within a class method.

Q6. What is inheritance in PHP?

ANS.  Inheritance allows a class to inherit properties and methods from another class.

Q7. What is a parent class and a child class?

ANS.  A parent class is the class from which properties and methods are inherited. A child class is the class that inherits from the parent class.

Q8. Explain the concept of method overriding.

ANS. Method overriding is when a child class defines a method with the same name and signature as a method in its parent class.

Q9. What is the difference between extends and implements in PHP?

ANS.  Extends is used to inherit from a single-parent class. implements is used to implement an interface, which defines a contract for a class to follow.

Q10. What is encapsulation in PHP?

ANS.  Encapsulation hides data within objects and provides controlled access.

Q11. How do you declare private, protected, and public properties and methods in PHP?

ANS. Use private, protected, and public keywords before property or method declarations.

Q12. What is the purpose of access modifiers?

ANS.  Access modifiers control the visibility of properties and methods from outside the class.

Q13. What is polymorphism in PHP?

ANS. Polymorphism allows objects of different classes to be treated as if they were of the same type.

Q14. Explain dynamic binding (late binding).

ANS. Dynamic binding determines the method to be called at runtime based on the object's type.

Q15. What is method overloading? Is it supported in PHP?

ANS.  Method overloading allows a class to have multiple methods with the same name but different parameters. It is not directly supported in PHP.

16. What is an abstraction in PHP?

ANS.  Abstraction defines a blueprint for objects, focusing on essential characteristics.

Q17. What is an abstract class?

ANS.  An abstract class is a class that cannot be instantiated directly. It contains at least one abstract method.

Q18. What is an interface?

ANS.  An interface defines a contract for classes to follow. It contains only public abstract methods and constants.

Q19. What is a trait in PHP?

ANS.  A trait is a mechanism for code reuse that can be composed into multiple classes.

Q20. What is a namespace in PHP?

ANS. A namespace is a way to organize code and avoid naming conflicts.

Q21. Explain the difference between static and non-static properties and methods.

ANS. Static members belong to the class itself, while non-static members belong to individual objects.

Q22. What is a magic constant?

ANS. A magic constant is a predefined variable that contains information about the current script or object.

Q23. What is a clone method?

ANS. The clone method creates a copy of an object.

Q24. Explain the concept of dependency injection.

ANS.  Dependency injection is a technique for passing dependencies to an object instead of the object creating them.

Q25. How do you write unit tests for PHP classes?

ANS.Use a testing framework like PHPUnit to create unit tests.

Q26. What is a debugger and how can you use it to debug PHP code?

ANS. A debugger is a tool that allows you to step through code, inspect variables, and identify errors.

Q27. Explain the importance of code quality and best practices in OOP.

ANS. Code quality and best practices improve readability, maintainability, and extensibility.

Q28. What is a design pattern?

ANS. A design pattern is a reusable solution to a common design problem.

Q29. Explain the Singleton pattern.

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

Q30. Explain the Factory pattern.

ANS. The Factory pattern creates objects without exposing the instantiation logic.

Q31. Explain the Observer pattern.

ANS. The Observer pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. 

Q32. Explain the Dependency Injection pattern.

ANS. The Dependency Injection pattern is a technique for passing dependencies to an object instead of the object creating them.

Q33. How can you improve the performance of your PHP OOP code?

ANS. Use caching, optimize database queries, avoid unnecessary object creation, and profile your code.

Q34. What is lazy loading?

ANS. Lazy loading is a technique for deferring the creation of objects until they are actually needed.

Q35. Explain the concept of composition over inheritance.

ANS. Composition is often preferred over inheritance because it promotes flexibility and avoids tight coupling.

Q36. What is the difference between static typing and dynamic typing?

ANS. Static typing checks types at compile time, while dynamic typing checks types at runtime.

Q37. What is a closure in PHP?

ANS. A closure is an anonymous function that can capture variables from its surrounding scope.

Q38. Explain the concept of dependency injection containers.

ANS. Dependency injection containers manage the creation and configuration of dependencies.

Q39. What is the difference between a class constant and a class property?

ANS. A class constant is defined using the const keyword and cannot be changed, while a class property can be modified.

Q40. How can you use OOP to model a shopping cart system?

ANS. Create classes for products, customers, orders, and shopping carts.

Q41. How can you use OOP to build a content management system (CMS)?

ANS. Create classes for pages, posts, users, and categories.

Q42. How can you use OOP to develop a web application framework?

ANS. Create classes for controllers, models, views, and routing.

Q43. How can you use OOP to implement a database abstraction layer?

ANS. Create classes for database connections, queries, and result sets.

Q44. How can you use OOP to develop a REST API?

ANS. Create classes for resources, requests, responses, and authentication.

Q45.  What is autoloading in PHP?

ANS.Autoloading is a mechanism that automatically loads classes when they are first used.

Q46. What is a trait composition conflict?

ANS. A trait composition conflict occurs when two traits have methods with the same name.

Q47. What is the purpose of the __clone() magic method?

ANS.The __clone() magic method is called when an object is cloned using the clone keyword.

Q48. What is the purpose of the __call() magic method?

ANS. The __call() magic method is called when a non-existent method is called on an object.

Q49. What is the purpose of the __toString() magic method?

ANS.The __toString() magic method is called when an object is converted to a string.

Q50. Explain the Facade pattern.

ANS.The Facade pattern provides a unified interface to a set of interfaces in a subsystem.