What is Class in Java? - Objects and Classes in Java {Explained}

A class in Java is a blueprint or template that defines the properties (fields) and behaviors (methods) that its objects will have. It's one of the core building blocks of object-oriented programming in Java.

Defining a Class

class Car {
    String brand;
    int speed;

    void accelerate() {
        speed += 10;
        System.out.println(brand + " is now going " + speed + " km/h");
    }
}

What is an Object?

An object is an actual instance of a class, created using the new keyword. While a class simply describes what a car looks like, an object represents one real, specific car with its own data.

Car myCar = new Car();
myCar.brand = "Toyota";
myCar.accelerate(); // Toyota is now going 10 km/h

Fields and Methods

• Fields (also called instance variables) store the state or data of an object
• Methods define the behavior or actions an object can perform
• Each object created from a class has its own separate copy of the instance fields

Constructors

A constructor is a special method used to initialize an object when it's created. It shares the same name as the class and has no return type.

class Car {
    String brand;
    Car(String brand) {
        this.brand = brand;
    }
}

Car myCar = new Car("Honda");

Multiple Objects from One Class

A single class can be used to create as many objects as needed, each with independent data.

Car car1 = new Car("Toyota");
Car car2 = new Car("Ford");

Class vs Object

• A class is a logical template; an object is a physical instance created from it
• No memory is allocated when a class is defined, only when an object is created
• A class is defined once but can produce many independent objects