Java Class and Object

Java is an object-oriented programming language where the building blocks are classes, fields, constructors, methods, and objects. Let’s understand each of them in detail.

Class:

A class is a blueprint for creating objects. It defines the fields (attributes) and methods (behavior) that an object will have.

Syntax:

class ClassName {
    // Fields
    // Constructors
    // Methods
}

Example

class Car {

// This is a class named Car

}

Fields:

Fields are variables declared within a class. They define the properties or attributes of the class and its objects.

Syntax:

class ClassName {
    DataType fieldName;  // Field declaration
}

Example

class Car {

String brand; // Field: brand of the car

int speed; // Field: speed of the car

}

Constructor:

A constructor is a special method used to initialize an object. It is automatically called when an object is created.

The name of the constructor must be the same as the class name.
It does not have a return type.

Syntax:

class ClassName {
    ClassName() {
        // Constructor logic
    }
}

Example

class Car {

String brand;

int speed;

// Constructor

public Car(String brand, int speed) {

this.brand = brand;

this.speed = speed;

}

Methods:

A method defines a behavior or functionality of the class. Methods are blocks of code that perform specific tasks and can return a value.

Syntax:

class ClassName {
    ReturnType methodName(Parameters) {
        // Method logic
    }
}

Example

class Car {

String brand;

int speed;

// Constructor

public Car(String brand, int speed) {

this.brand = brand;

this.speed = speed;

}

// Method to display car details

public void displayDetails() {

System.out.println("Brand: " + brand + ", Speed: " + speed + " km/h");

}

Object:

An object is an instance of a class. It represents a specific entity that has its own state and behavior defined by the class.

Syntax:

ClassName objectName = new ClassName();

Example

public class Main {

public static void main(String[] args) {

// Creating an object of the Car class

Car myCar = new Car("Toyota", 120);

// Accessing the object's method

myCar.displayDetails(); // Output: Brand: Toyota, Speed: 120 km/h

}

Try it yourself

Multiple Objects:

You can create multiple objects of one class:

Example

// Main class to use the Car class

public class Main {

public static void main(String[] args) {

// Creating objects of the Car class

Car car1 = new Car("Toyota", 120);

Car car2 = new Car("Honda", 100);

// Accessing methods of the Car objects

car1.displayDetails(); // Output: Brand: Toyota, Speed: 120 km/h

car2.displayDetails(); // Output: Brand: Honda, Speed: 100 km/h

car1.accelerate(30); // Output: Toyota accelerated to 150 km/h

car2.accelerate(20); // Output: Honda accelerated to 120 km/h

}

Try it yourself

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