🟢 Basic OOP Interview Questions

1. What is OOP in PHP?

OOP (Object-Oriented Programming) is a programming paradigm based on classes and objects. It helps organize code using:

Encapsulation
Inheritance
Polymorphism
Abstraction

2. What is a Class and Object?

Class → Blueprint of an object
Object → Instance of a class

class Car {
    public $brand = "BMW";
}$car = new Car(); // object

3. What is a Constructor?

A constructor is a special method called automatically when an object is created.

class Test {
    public function __construct() {
        echo "Object Created";
    }
}

4. What is a Destructor?

It is called when an object is destroyed.

public function __destruct() {
    echo "Object Destroyed";
}

🟡 Intermediate Questions

5. What is Encapsulation?

Wrapping data and methods into a single unit and restricting access using:

private
protected
public

6. What is Inheritance?

Acquiring properties and methods of another class.

class ParentClass {}
class ChildClass extends ParentClass {}

7. What is Polymorphism?

Same method, different behavior.

class A { function test(){ echo "A"; } }
class B extends A { function test(){ echo "B"; } }

8. What is Abstraction?

Hiding internal details and showing only functionality using:

Abstract classes
Interfaces

9. Difference between Abstract Class and Interface?

Feature	Abstract Class	Interface
Methods	Both abstract & normal	Only abstract
Properties	Allowed	Not allowed
Multiple Inheritance	No	Yes

10. What are Access Modifiers?

Modifier	Access
public	Everywhere
private	Same class
protected	Class + child

🔵 Advanced Questions

11. What is Late Static Binding?

Allows static methods to be resolved based on the called class, not the declaring class.

class A {
    public static function test() {
        static::who();
    }
    public static function who() {
        echo "A";
    }
}class B extends A {
    public static function who() {
        echo "B";
    }
}B::test(); // Output: B

12. What are Magic Methods?

Special methods starting with __

Examples:

__construct()
__destruct()
__get()
__set()
__toString()

13. What is Dependency Injection?

Passing dependencies to a class instead of creating inside.

class DB {}
class User {
    private $db;
    public function __construct(DB $db) {
        $this->db = $db;
    }
}

14. What is Trait in PHP?

Used to reuse code in multiple classes.

trait Logger {
    public function log() {
        echo "Logging...";
    }
}

15. What is Namespace?

Used to avoid class name conflicts.

namespace App\Models;
class User {}

🔴 Scenario-Based Questions (Very Important 🚀)

16. How would you design a login system using OOP?

User class
Auth controller
Database class
Password hashing

17. How do you handle database in OOP PHP?

Use PDO
Create DB class
Use Singleton or Dependency Injection

18. What is MVC?

Model → Data
View → UI
Controller → Logic

🎯 Pro Interview Tips

Always explain with real examples
Mention security (password_hash, PDO)
Talk about scalability & clean code
Avoid procedural style in answers

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important Object-Oriented PHP (OOP) interview questions with answers