🟢 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

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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

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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";
    }
}

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4. What is a Destructor?

It is called when an object is destroyed.

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

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🟡 Intermediate Questions

5. What is Encapsulation?

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

• private
• protected
• public

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6. What is Inheritance?

Acquiring properties and methods of another class.

class ParentClass {}
class ChildClass extends ParentClass {}

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7. What is Polymorphism?

Same method, different behavior.

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

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8. What is Abstraction?

Hiding internal details and showing only functionality using:

• Abstract classes
• Interfaces

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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

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10. What are Access Modifiers?

Modifier	Access
public	Everywhere
private	Same class
protected	Class + child

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🔵 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

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12. What are Magic Methods?

Special methods starting with __

Examples:

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

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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;
    }
}

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14. What is Trait in PHP?

Used to reuse code in multiple classes.

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

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15. What is Namespace?

Used to avoid class name conflicts.

namespace App\Models;
class User {}

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🔴 Scenario-Based Questions (Very Important 🚀)

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

• User class
• Auth controller
• Database class
• Password hashing

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17. How do you handle database in OOP PHP?

• Use PDO
• Create DB class
• Use Singleton or Dependency Injection

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18. What is MVC?

• Model → Data
• View → UI
• Controller → Logic

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🎯 Pro Interview Tips

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