Best 30 Advanced PHP OOPs Interview Questions and Answers


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Mostly Asked Advanced PHP OOPs Interview Questions and Answers

We are listing the most asked Best 30 Advanced PHP OOPs Interview Questions and Answers for you to gain the best job.

Question 1:- What is OOP?

Answer:- OOP stands for Object-Oriented Programming. It is a programming paradigm that is used to design your application. In other words, programs are considered as a collection of objects. Each object is an instance of a class.

Question 2:- What are the basic concepts of OOPs?

Answer:- Basic concepts of OOPs are as follows:-

  • Class
  • Object
  • Polymorphism
  • Inheritance
  • Encapsulation
  • Abstraction

Question 3:- What is the difference between a class and an object?

Answer:- Difference between a class and an object:

It is a template for creating or initializing objects within a program.An object is an instance of a class.
Class is declared by using the class keyword.The object is created through the “new” keyword.
The formation of a class does not allocate memory.When an object is created, it consumes memory.
It is declared by once.Multiple objects can create using the class.
It is a logical entity.It is a physical entity.

Question 4:- What are the constructor and destructor?

Answer:- Constructor: Constructor is automatically called when the object is initialized.


class Example1
      public function __construct()
           echo "Hello";
$A = new Example1();



Destructor: Destructor is exactly the reverse of the constructor method. It is called when an instance of the class is deleted from the memory. They do not have any return value. It is also used during the finish of the execution of the php script as well as the execution control leaves the block.

function __destruct()
     // destroying the object or clean up resources here 

Question 5:- Explain the types of constructors?

Answer:- There are 3 types of constructors:-

  • Default Constructor:- Default constructor has no parameters.
  • Parameterized Constructor:- Parameterized constructor accepts the arguments or parameters. You can assign the values to the variables during the object creation.
  • Copy Constructor:- It is a member function that initializes an object of the same class. It allows the address of the other objects as a parameter.

Question 6:- What is the difference between Constructor and Destructor in PHP?

Answer:- Difference between Constructor and Destructor in PHP:

One or more arguments are accepted.It’s void. No arguments are passed.
It is automatically invoked when the object is created.When the object is destroyed, the destructor is called automatically.
It is used to initialize the instance of a class.It is used to terminate the existing objects to free up memory for new accommodation.
Initialize the data members of the class.Used to make the objects perform some task before it is destroyed.
Constructors can be overloaded.Destructors can not be overloaded.
It allocates memory.It deallocates memory.

Question 7:- What are the access modifiers in php?

Answer:- Access Modifier describes the scope of the method and variables that can be accessed from different objects as well as classes.

  • Public:- Public method or variable can be accessed from anywhere, whether that code is inside or outside the class.
  • Protected:- Protected method or variable can not be accessed outside the class by code. Only the base class or child class can access the properties.
  • Private:- Private method or variable can be accessed within the class.

Question 8:- What is the interface in php?

Answer:- Interface contains no data variables rather than function prototypes. It is defined by using the “interface” keyword. The “implements” operator is used to extend the interface. You can inherit all the interface classes at the time of extension. All the interfaces are separated by a (,) comma. All the methods must be implemented within a child class. The class implements an interface that uses the same method signatures as defined in an interface.

Question 9:- What is abstraction?

Answer:- Abstract is one of the most essential features of OOPS. It allows the clients to show only needed details of the objects, not the internal constructors of the objects. It is defined by using the -“abstract” keyword. “extends” operator is used to extending the abstract class. Any class that contains a single abstract method must also be declared as abstract.

Question 10:- What is polymorphism in PHP? Explain its types?

Answer:- Polymorphism can be defined as “One thing, can use in different forms”. In other words, it assigns the behavior or value in a subclass to something that was already declared in the main class. It can redefine methods for derived classes.

Question 11:- What is the difference between Method Overloading and Method Overriding in php?

Answer:- Difference between Method Overloading and Method Overriding:

Method OverloadingMethod Overriding
It performs within the class.It performs in the derived class.
Method Overloading is also known as static binding.Method Overriding is also known as dynamic binding.
It is an example of compile-time polymorphism.It is an example of run time polymorphism.
The parameter must be different in method overloading.Parameters must be the same in method overriding.
It helps to extend functionalities.It helps to overwrite or change the existing functionalities.
Static Method can be overloaded.Non Static Methods can be overloaded.

Question 12:- Differentiate between concrete class and abstract class?

Answer:- Difference between concrete class and abstract class:

Concrete ClassAbstract Class
It is used for specific requirements.It is used to meet the common requirement.
Objects of concrete class can create directly.Objects of abstract class can not create directly.
It contains fully defined methods of implemented methods.It has both defined methods and undefined methods.
The “Class” keyword is used to define the method.The “Abstract” keyword is used to define the method.

Question 13- What is static and dynamic binding?

Answer:-Static Binding: The binding that can be resolved by the compiler at compile-time, is called static binding. Static Binding is also known as early binding. All static, private, and final methods are binding at compile time because all such methods can not be overridden. And these methods can be accessed by objects of local class at compile time.

class student
public static $my_name = 'Joe';
    	public static function getName()
       		return "The name of the student is : " . self::$my_name;
    	public static function getAge()
       		echo static::getName();
class Professor extends student
  	public static function getName()
       		return "The name of the student is:". self::$my_name . " and their age is 24.";
echo "\n";


The name of the student is: Joe

The name of the student is: Joe and their age is 24.

Dynamic Binding: Dynamic binding is known as dynamic binding when the compiler does not decide which method to be called. Dynamic binding is also known as late binding. Both parent and child classes have the same method in the overriding method. However, the type of object determines which method is to be executed.

class Animal
  	void eat()
System.out.println("animal is eating...");
class Dog extends Animal
  	void eat()
System.out.println("dog is eating...");
public static void main(String args[])
   		Animal a=new Dog();;  


Dog is eating…

Question 14:- What is the difference between a class and interface?

Answer:- Difference between a class and interface:

The “class” keyword is used to create a class.The “interface” keyword is used to create an interface.
Classes can not support multiple inheritance.Interface support multiple inheritance.
A class can inherit another class.It can not inherit a class.
It can contain constructors.Constructors are not allowed in the interface.
Variables and methods can be declared by using any access modifier (public, private, protected, default).All the variables are declared as public.
It contains abstract methods.It can not contain abstract methods.

Question 15:- What are class constants?

Answer:- When we declare the variable with the const keyword, then it is known as class const. The class constant is case-sensitive and unchangeable once it is declared. It is declared inside the class definition.

Question 16:- What are Traits?

Answer:- Traits are the mechanism to reuse the code in a single inheritance language in PHP. It allows the developers to reuse a set of methods in several independent classes living in different class hierarchies. It reduces the complexity and avoids the typical program associated with multiple inheritances with the combination of traits and classes.

Question 17:- What are static methods?

Answer:- When we declare the method with the static keyword, it is known as the static method.

Question 18:- Multiple inheritance not supported in PHP. Why?

Answer:- When a child class in OOP (Object-Oriented Programming) accesses the characteristics and features of more than one parent class, it is called Multiple inheritances. PHP does not support multiple inheritance because it causes ambiguity and confuses the compiler. In the other words, if the parent class has the same method name, then the compiler will confuse to decide that the method being called belongs to which class.

Question 19:- What is Scope Resolution Operator?

Answer:- The Scope Resolution Operator defines a double colon sign (::). Basically, it allows a way of a class’s static, constant, and overridden properties or methods. It’s also known as “Paamayim Nekudotayim”.

Question 20:- What is UML?

Answer:- UML stands for Unified Modeling Language. It is a standardized modeling language to visualize the way a system has been designed. Moreover, UML helps software engineers, design and analysis, and system architects with modeling.

Question 21:- What is the use of static keywords in PHP?

Answer:- Static keyword is used to access static methods as well as static variables without creating an object.

Question 22:- What is Type Hinting in PHP?

Answer:- Type hinting is used to specify the expected data type (arrays, objects, interface, etc.) for an argument in the function declaration. It is also known as the type declaration. Moreover, it provides results in better code organization as well as improved the error messages.

Question 23:- What is data modeling?

Answer:- Data Modeling is a step-by-step process of creating a data model to store the data in a database. It is the conceptual representation of data objects and the association between different data objects.

Question 24:- What is inheritance?

Answer:- Inheritance is an important concept of OOP (Object Oriented Programming). It is a mechanism in PHP by which the subclass inherits all the properties of the superclass.

Types of Inheritance:-

  • Single Inheritance
  • Multilevel Inheritance
  • Hierarchical Inheritance
  • Hybrid Inheritance

Question 25:- What is encapsulation?

Answer:- Encapsulation is a concept of OOPS (Object Oriented Programming System) in PHP. It wraps up all the member variables and methods in a single unit (class). All the hidden data are restricted to the members of that class.

Question 26:- What is the final class and the final method in PHP?

Answer:- Final Class: We can declare the final class with the help of the final keyword in PHP. After the declaration of class as final, then we restrict other classes to inherit or extend it. If another class attempts to extend the final class, then you will get a compilation error.

Final Method: We can declare the final method by adding the final keyword before the method name. The final method in PHP can not override in the subclass.

Question 27:- What is “$this” in OOPs?

Answer:- “$this” refers to the current object of a class.

Question 28:- What is a member variable?

Answer:- Member variables are defined in a class. These variables are not visible outside the class but they can access through member functions. After the creation of an object at once, these variables are also known as attributes of the object.

Question 29:- What is member function?

Answer:- Member functions are those functions that define inside the class and use to access the object data

Question 30:- What is namespace in php?

Answer:- Namespace is the way of encapsulating the items to reuse the same name without name conflicts. The “Namespace” keyword is used to declare namespaces. It can contain valid PHP code. It declares the namespace at the top of the file before any other code – with one exception: the declare keyword. You can declare namespace globally but without using any name.

So, hope you get the Best 30 Advanced PHP OOPs Interview Questions and Answers. It will help you to crack the PHP developer interview as a fresher or an experienced.

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