Adding content to 101-paradigm-features

src/roadmaps/software-design-architecture/content/102-object-oriented-programming/101-paradigm-features/100-abstract-classes.md

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-# Abstract classes
+# Abstract Classes
+
+An abstract class is a class in object-oriented programming (OOP) that cannot be instantiated. Instead, it serves as a template or blueprint for other classes to inherit from. An abstract class can contain both abstract and non-abstract methods (abstract methods are methods that do not have any implementation, they just have a signature).
+
+Abstract classes are used to provide a common interface and implementation for a group of related classes. They are also used to define common behavior that must be implemented by all subclasses. A subclass that inherits from an abstract class is called a concrete class, and it must provide an implementation for all the abstract methods declared in the parent class.
+
+Learn more from the following resources:
+
+- [What is an Abstract Class in Object Oriented Programming](https://computinglearner.com/abstract-class-in-object-oriented-programming/)

src/roadmaps/software-design-architecture/content/102-object-oriented-programming/101-paradigm-features/101-concrete-classes.md

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-# Concrete classes
+# Concrete Classes
+
+A concrete class is a class in object-oriented programming (OOP) that can be instantiated, meaning objects can be created from it. A concrete class is a class that provides an implementation for all of the abstract methods declared in its parent class, if it inherits from an abstract class. A concrete class can also be a class that does not inherit from an abstract class, in that case it can have implementation for all of its methods.
+
+Concrete classes are used to provide specific implementation details for a group of related classes that inherit from a common abstract class. They are also used to define unique behavior for a specific class. A concrete class can have its own methods and variables, and can also override the methods of its parent class.
+
+Learn more from the following resources:
+
+- [Concrete class in Java](https://www.geeksforgeeks.org/concrete-class-in-java/)
+- [Overview of Concrete Class](https://www.sciencedirect.com/topics/computer-science/concrete-class)

src/roadmaps/software-design-architecture/content/102-object-oriented-programming/101-paradigm-features/102-scope-visibility.md

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-# Scope visibility
+# Scope Visibility
+
+Scope visibility refers to the accessibility or visibility of variables, functions, and other elements in a program, depending on the context in which they are defined. In object-oriented programming (OOP), scope visibility is controlled through the use of access modifiers, such as "public," "private," and "protected."
+
+- Public: A public element can be accessed from anywhere in the program, both within the class and outside of it.
+- Private: A private element can only be accessed within the class in which it is defined. It is not accessible to other classes, even if they inherit from the class.
+- Protected: A protected element can only be accessed within the class and its subclasses.
+
+There are variations of scope visibility based on the programming language, but these are the most common.
+
+Learn more from the following resources:
+
+- [Scope, Visibility and Lifetime of Variables](https://www.youtube.com/watch?v=GQn46bSZE1g)

src/roadmaps/software-design-architecture/content/102-object-oriented-programming/101-paradigm-features/103-interfaces.md

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-# Interfaces
+# Interfaces
+
+In object-oriented programming (OOP), an interface is a contract or a set of methods that a class must implement. It defines a common set of methods that a class must provide, but it does not provide any implementation details. An interface can include both method signatures and constants.
+
+Interfaces are used to define a common behavior for a group of related classes, and to provide a way for objects of different classes to be treated polymorphically. A class that implements an interface must provide an implementation for all of the methods declared in the interface. A class can implement multiple interfaces, but can only inherit from one base class.
+
+Learn more from the following resources:
+
+- [Fundamental concepts: What's an Interface?](https://www.youtube.com/watch?v=o1jBgdhQsGo)

src/roadmaps/software-design-architecture/content/102-object-oriented-programming/101-paradigm-features/index.md

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-# Paradigm features
+# Paradigm Features
+
+Object-oriented programming (OOP) is a programming paradigm that is based on the concept of "objects," which are instances of a class. OOP has several key features that distinguish it from other programming paradigms:
+
+1. Encapsulation
+2. Inheritance
+3. Polymorphism
+4. Abstraction
+5. Classes
+6. Objects
+7. Interfaces
+8. Dynamic binding
+9. Message passing
+
+These features provide OOP with the ability to model real-world objects and their interactions, making it well-suited for creating complex and large-scale software systems.
+
+
+Learn more from the following resources:
+
+- [Overview of Object-Oriented Paradigm](https://www.tutorialspoint.com/software_architecture_design/object_oriented_paradigm.htm)