Which of the following is/are true for an abstract class?i) Abstract classes in PHP are declared with the help of abstract keyword.ii) A class is declare abstract by using the keyword implements.iii) It is a class that really isn’t supposed to ever be instantiated but instead serves as a base class.iv) Attempting to instantiate an abstract class results in an error.

PHP introduced object-oriented programming features since version 5.0. Object-Oriented programming is one of the most popular programming paradigms based on the concept of objects and classes. Object-oriented programming (OOP) is a programming paradigm in PHP that focuses on data and its associated functions. It involves creating objects that contain both data and functions. OOP has several advantages over procedural programming, including: Maintenance: OOP helps to keep code DRY ("Don't Repeat Yourself") and makes it easier to maintain, modify, and debug. Reusability: OOP makes it... Show more

PHP introduced object-oriented programming features since version 5.0. Object-Oriented programming is one of the most popular programming paradigms based on the concept of objects and classes.
Object-oriented programming (OOP) is a programming paradigm in PHP that focuses on data and its associated functions. It involves creating objects that contain both data and functions. OOP has several advantages over procedural programming, including:
Maintenance: OOP helps to keep code DRY ("Don't Repeat Yourself") and makes it easier to maintain, modify, and debug.
Reusability: OOP makes it possible to create full reusable applications with less code.
Scalability: OOP facilitates scalability, as new classes and objects can be added without affecting existing code. 

OOP revolves around the inheritance, polymorphism, encapsulation, and abstraction concepts.

The four pillars of OOP are abstraction, encapsulation, inheritance, and polymorphism. By using these four pillars of OOPs, developers can create programs that are powerful, maintainable, and extensible. 
PHP is a versatile language that can be used for many tasks, including: Server-side development, Command-line usage, and Application development. 
Here are some good object-oriented habits for PHP: Use interfaces, Use public accessors, Be proactive about validating arguments, and Throw exceptions. 

Here are some things you can do with classes and objects in PHP:
Create an object from a class: Use the new keyword
Access a class's properties and methods: Use the object and -> operator
Class member variables: Hold specific data
Class member properties: Can be public, private, or protected
Class member methods: Can be public, private, or protected
Class member constants: Special entities that remain fixed on an individual class basis 

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