20 OOP PHP Interview Questions and Answers

If you’re interviewing for a PHP development position, you’ll need to be well-versed in object-oriented programming (OOP). OOP is a programming paradigm that uses objects and their interactions to design applications. Many PHP developers use OOP because it helps promote code reusability and maintainability.

In this article, we’ll review some common OOP PHP interview questions. By preparing for these questions, you’ll be able to demonstrate your knowledge of OOP concepts and impress the interviewer.

OOP PHP Interview Questions and Answers

Here are 20 commonly asked OOP PHP interview questions and answers to prepare you for your interview:

1. What is Object Oriented Programming (OOP)?

OOP is a programming paradigm that is based on the concept of objects, which are data structures that contain both data and methods. OOP is designed to make code more modular, reusable, and easy to understand.

2. Can you explain the difference between procedural and object-oriented programming?

Procedural programming is a programming paradigm that follows a linear sequence of commands. Object-oriented programming, on the other hand, is a programming paradigm that is organized around objects rather than commands. In OOP, objects are used to represent data and the methods are used to manipulate that data.

3. How do objects in PHP differ from other types of variables like strings, arrays, or integers?

Objects in PHP are instances of classes, which are templates for creating objects. This means that objects can have their own methods and properties, which are defined by the class. Other types of variables, like strings, arrays, or integers, do not have their own methods and properties and are not instances of any class.

4. What are some advantages that OOP offers over procedural programming?

OOP offers a number of advantages over procedural programming, including the ability to create objects that can be reused in other programs, the ability to encapsulate data and code together, and the ability to create inheritance hierarchies.

5. What are the building blocks of an OOP program?

The building blocks of an OOP program are objects, classes, and inheritance. Objects are the basic units of an OOP program, and they are usually created from classes. Inheritance is the process by which one class can inherit the attributes and methods of another class.

6. How can you create a class in PHP?

You can create a class in PHP by using the class keyword, followed by the name of the class. The class definition must be placed within curly braces.

7. What’s the purpose of using a constructor to initialize an object? Why not use a regular method instead?

The purpose of using a constructor to initialize an object is to ensure that all of the necessary data is set up before the object is used. This can be important when working with complex objects that need to be in a specific state before they can be used. Using a regular method instead of a constructor can lead to problems if the method is not called before the object is used, as the object may not be in the correct state.

8. If a class has multiple constructors defined on it, will its child classes inherit them all?

No, child classes will only inherit the constructor defined in the parent class. If multiple constructors are defined in the parent class, then the child class will only inherit the most recently defined constructor.

9. Can you explain the difference between a property and a field in the context of an OOP model?

A property is a value that is associated with an object, while a field is a value that is associated with a class. In other words, a property is specific to an individual object, while a field is shared by all objects of a given class.

10. What are the different access modifiers in PHP and what do they mean?

The different access modifiers in PHP are public, private, and protected. Public means that the member can be accessed from anywhere, private means that the member can only be accessed from within the class, and protected means that the member can only be accessed from within the class or from a child class.

11. When should we use protected properties/methods in a class definition?

We should use protected properties/methods when we want to make them available to child classes, but not to the general public. By making them protected, we are ensuring that only child classes can access them, which helps to keep our code more secure.

12. Is it possible to change the scope of a member variable after creating an instance of the class in which it exists?

No, it is not possible to change the scope of a member variable after creating an instance of the class in which it exists. The only time you can change the scope of a member variable is when you declare it inside of the class.

13. What is inheritance? Can you give me an example of how it works?

Inheritance is a concept in OOP whereby one class can inherit the properties and methods of another class. This allows for code reuse and helps to keep your code DRY (Don’t Repeat Yourself). A common example of inheritance is a parent class (e.g. “Animal”) and a child class (e.g. “Dog”). The child class will inherit all of the properties and methods of the parent class, but can also have its own unique properties and methods.

14. What is polymorphism? Can you give me an example of how it works?

Polymorphism is the ability of an object to take on different forms. In PHP, this means that a class can have multiple methods with the same name, but each method will have a different number of parameters. For example, you could have a class with two methods named “display”. One method might take no parameters and simply output the data to the screen, while the other might take a parameter specifying where to output the data (e.g. to a file).

15. What is encapsulation? Can you give me an example of how it works?

Encapsulation is the process of hiding information within an object so that it can only be accessed by authorized methods. For example, a class can have private methods that can only be accessed by other methods within the same class. This ensures that data is only accessed and modified in the way that the class author intended.

16. What is abstraction? Can you give me an example of how it works?

Abstraction is the process of hiding the details of an implementation from the user. In PHP, this can be done by using the abstract keyword to create an abstract class, which can then be extended by other classes. An example of this would be an abstract class that defines a method for connecting to a database. The details of the implementation (i.e. the actual code for connecting to the database) would be hidden from the user, and the user would only need to know the method signature in order to use it.

17. What is the difference between dependency injection and factory design pattern?

The main difference between dependency injection and factory design pattern is that dependency injection is a technique for achieving loose coupling between objects and their dependencies, while factory design pattern is a creational design pattern that provides an interface for creating objects.

18. What libraries would be useful for OOP development in PHP?

There are a few different libraries that can be useful for OOP development in PHP. The most popular one is probably the PEAR library, which provides a lot of helpful tools and classes for OOP development. Other libraries include the Zend Framework and the Symfony Framework, which both provide a lot of helpful functionality for OOP development.

19. What is your opinion about Zend Framework 1 vs Zend Framework 2?

I think that both Zend Framework 1 and 2 are great frameworks. They both have their pros and cons, but I think that Zend Framework 2 is a bit more user-friendly and easier to learn.

20. If a class inherits two methods with the same name from its parent class and both have the same number of parameters, then what happens when you try to instantiate this class?

If a class inherits two methods with the same name from its parent class and both have the same number of parameters, then the child class will use the method that is defined last in the code.