JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III OBJECT ORIENTED PROGRAMMING THROUGH JAVA Previous Question Paper (August/September - 2021 - R18)

Object-Oriented Programming (OOP) is a paradigm based on the concept of objects which contain data and code. The core features are:

• Classes and Objects: A class is a blueprint for objects. An object is an instance of a class that encapsulates state (fields) and behavior (methods).
• Encapsulation: The mechanism of wrapping data and the methods that operate on the data into a single unit, restricting direct access to some components to prevent accidental modification.
• Abstraction: Hiding complex implementation details and showing only the essential features of an object to the user.
• Inheritance: A mechanism where a new class acquires the properties and behaviors of an existing class, promoting code reusability.
• Polymorphism: The ability of an object or method to take on multiple forms, typically achieved through method overloading (compile-time) and method overriding (runtime).

Java provides four levels of access control to manage the visibility of classes, variables, and methods:

• Private: The most restrictive level. Members are accessible only within the class they are declared in. Example:
  private int data;
• Default (Package-private): If no modifier is specified, the member is accessible only within the same package. Example:
  void display() { ... }
• Protected: Accessible within the same package and by subclasses in different packages. Example:
  protected void show() { ... }
• Public: The least restrictive level. Members are accessible from any other class in the application. Example:
  public void execute() { ... }

These modifiers ensure data integrity and security by controlling the scope of access across the application hierarchy.