Object-Oriented Programming

Java is fundamentally an object-oriented language. Almost everything in Java is an object — instances of classes that bundle data (fields) and behaviour (methods) together. This lesson covers classes, objects, constructors, encapsulation, and the this keyword.

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Classes and Objects

A class is a blueprint; an object is an instance of that blueprint.

public class Car {
    // Fields (instance variables)
    String make;
    String model;
    int year;

    // Method
    void describe() {
        System.out.println(year + " " + make + " " + model);
    }
}

Creating Objects

Car myCar = new Car();
myCar.make = "Toyota";
myCar.model = "Corolla";
myCar.year = 2024;
myCar.describe();  // "2024 Toyota Corolla"

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Constructors

A constructor is a special method called when you create an object with new. It initialises the object's fields.

public class Car {
    String make;
    String model;
    int year;

    // Constructor
    public Car(String make, String model, int year) {
        this.make = make;
        this.model = model;
        this.year = year;
    }

    void describe() {
        System.out.println(year + " " + make + " " + model);
    }
}

// Usage:
Car myCar = new Car("Toyota", "Corolla", 2024);
myCar.describe();