Object-Oriented Programming, or OOP, is a programming paradigm based on the concept of objects. Objects contain both data, which we call attributes or properties, and code, which we call methods or behaviors. Think of a class as a blueprint that defines what objects will look like and how they will behave. From this blueprint, we can create multiple objects, each representing a real-world entity with its own state and behavior.
Encapsulation is one of the fundamental principles of object-oriented programming. It involves bundling data and methods that operate on that data into a single unit, which is the class. Encapsulation also restricts direct access to some of an object's components, providing data protection and security. We achieve this through access modifiers like private, which restricts access to the class only, public which allows access from everywhere, and protected which allows access from the same package and subclasses. This controlled access helps maintain code integrity and makes our programs more maintainable.
Inheritance is a fundamental concept in object-oriented programming that allows one class to acquire properties and behaviors from another class. We call the class that provides the properties the parent class or superclass, and the class that receives them the child class or subclass. In Java, we use the extends keyword to establish this relationship. For example, if we have an Animal parent class, we can create Dog and Cat child classes that inherit all the properties and methods from Animal. This promotes code reusability and helps establish hierarchical relationships between classes. Java supports single inheritance, meaning a class can only extend one parent class, but it can implement multiple interfaces.
Polymorphism, meaning many forms, is a powerful feature that allows objects of different classes to be treated as objects of a common superclass. In Java, we have two main types of polymorphism. First is method overloading, which is compile-time polymorphism where we define multiple methods with the same name but different parameters. Second is method overriding, which is runtime polymorphism where a subclass provides a specific implementation of a method that is already defined in its parent class. For example, if we have a Shape class with a draw method, different subclasses like Circle, Square, and Triangle can each provide their own implementation of the draw method, allowing the same method call to produce different behaviors.
To summarize what we have learned about object-oriented programming in Java: OOP organizes code around objects that contain both data and behavior. Encapsulation protects our data and provides controlled access through methods. Inheritance enables code reuse by allowing classes to inherit properties from parent classes. Polymorphism allows one interface to represent different underlying data types. Together, these four principles make Java programs more maintainable, reusable, and scalable.