Welcome to Object-Oriented Programming in Java! OOP is a fundamental programming paradigm that revolutionized software development. It organizes code around objects and classes, making programs more modular, reusable, and easier to maintain. A class serves as a blueprint or template, while objects are instances created from that blueprint. This approach provides four core principles that we'll explore: Encapsulation, Inheritance, Polymorphism, and Abstraction.
Now let's explore classes and objects in detail. A class serves as a blueprint that defines the structure and behavior of objects. It contains three main components: attributes which store data, methods which define behaviors, and constructors which initialize new objects. In this Java example, we define a Car class with private attributes for brand and year, a constructor to initialize these values, and methods to interact with the object. Objects are created using the 'new' keyword, making each instance independent with its own data.
Encapsulation is one of the fundamental principles of object-oriented programming. It involves bundling data and methods together within a class while controlling access to them. Private attributes hide the internal data from external access, while public methods provide a controlled interface for interaction. This approach protects data integrity by preventing unauthorized modifications and ensures that objects maintain a consistent state. Getters and setters allow controlled access to private data, enabling validation and maintaining encapsulation principles.
Inheritance is another fundamental principle of object-oriented programming that promotes code reusability. It allows a class to inherit properties and methods from another class using the 'extends' keyword in Java. The parent class, also called superclass, defines common attributes and behaviors, while child classes, or subclasses, inherit these features and can add their own specific functionality. For example, a Vehicle class might define basic methods like start and stop, while Car and Bike classes inherit these methods and add their own unique behaviors like honk or pedal. This creates a hierarchical relationship that reduces code duplication.
Finally, let's explore polymorphism and abstraction. Polymorphism allows objects of different types to respond to the same method call in their own unique way. For example, different shapes can all implement a draw method, but each shape draws itself differently. Abstraction hides complex implementation details and shows only essential features through abstract classes and interfaces. These principles work together to create flexible and maintainable code. When you call the same method on different objects, the correct implementation is chosen at runtime through dynamic method dispatch, making your code more adaptable and easier to extend.