Java Classes and Objects

Java is an object-oriented programming language. Objects represent entities that have both state and behavior. For example, a bicycle is an object with:

• States: idle, first gear, etc.
• Behaviors: braking, accelerating, etc.

Java Class

A class is a blueprint for creating objects. It defines the state (fields) and behavior Methods of the objects.

class Bicycle {
  // state or field
  private int gear = 5;

  // behavior or method
  public void braking() {
    System.out.println("Working of Braking");
  }
}

Creating Objects

An object is an instance of a class. You can create multiple objects from a single class using the new keyword.

Bicycle sportsBicycle = new Bicycle();
Bicycle touringBicycle = new Bicycle();

Accessing Members

Use the object name with the . operator to access fields and methods.

sportsBicycle.gear;
sportsBicycle.braking();

Example 1: Class and Objects

class Lamp {
  boolean isOn;

  void turnOn() {
    isOn = true;
    System.out.println("Light on? " + isOn);
  }

  void turnOff() {
    isOn = false;
    System.out.println("Light on? " + isOn);
  }
}

public class Main {
  public static void main(String[] args) {
    Lamp led = new Lamp();
    Lamp halogen = new Lamp();

    led.turnOn();
    halogen.turnOff();
  }
}

Output

Output:
Light on? true
Light on? false

Example 2: Objects Inside the Same Class

class Lamp {
  boolean isOn;

  void turnOn() {
    isOn = true;
    System.out.println("Light on? " + isOn);
  }

  public static void main(String[] args) {
    Lamp led = new Lamp();
    led.turnOn();
  }
}

Output

Output:
Light on? true