How to create Multiple class in java Program -

class Computer {
  Computer() {
    System.out.println("Constructor of Computer class.");
  }

  void computer_method() {
    System.out.println("Power gone! Shut down your PC soon...");
  }

  public static void main(String[] args) {
    Computer my = new Computer();
    Laptop your = new Laptop();

    my.computer_method();
    your.laptop_method();
  }
}

class Laptop {
  Laptop() {
    System.out.println("Constructor of Laptop class.");
  }

  void laptop_method() {
    System.out.println("99% Battery available.");
  }
}

Step-by-Step Explanation:

This software is divided into two classes: Computer and Laptop. In this example, it explains how inheritance is implemented in Java through the Laptop class which is a subclass of Computer.

Class: Computer

class Computer {

Computer() {

System.out.println(“Constructor of Computer class.”);

}

void computer_method () {

System.out.println(“Power gone! Shut down your PC soon.”);

}

1. Constructor of Computer Class:

The class constructor Computer() is declared. A class’s constructor is automatically invoked whenever a class instance or object is being created.
The constructor prints the message “Constructor of Computer class.” whenever the object of the Computer class is created.

2. Method computer_method():

This is another typical instance method of the class Computer. On being invoked, it prints “Power gone! Shut down your PC soon.”

Class: Laptop (Sub-class of Computer)

class Laptop

{

Laptop()

{

System.out.println(“Constructor of Laptop class.”);

}

void laptop_method() {

System.out.println(“99% Battery available.”);

}

1. Constructor of Laptop Class:

The constructor Laptop() is called when an object of the Laptop class is created. It prints the message “Constructor of Laptop class.”.

2. Method laptop_method():

This method prints the message “99% Battery available.” when invoked. This method is defined in the Laptop class.

Main Method (Entry Point of Program)

public class Main {

public static void main(String[] args) {

Computer my = new Computer();

Laptop your = new Laptop();

my.computer_method();

your.laptop_method();

}

1. Defining Object for Computer Class:

The line Computer my = new Computer(); declares an instance of the class Computer.
When new Computer() is invoked, the constructor of the Computer class is invoked, printing:

Constructor of Computer class.

2. Instantiating Laptop Class:

Laptop your = new Laptop(); instantiates the Laptop class.

When new Laptop() is invoked, it calls the Laptop class’s constructor, printing the following output:

Constructor of Laptop class.

Displayed on a console

3. Invocation of computer_method() on Computer Object

my.computer_method(); invokes computer_method() of Computer class from my object

This program prints

Power gone! Shutdown your PC now.

4. Calling laptop_method() on Laptop Object:

your.laptop_method(); calls the laptop_method() of the Laptop class using the your object.

The method laptop_method() prints:

99% Battery available.

Final Output:

Power gone! Shut down your PC soon.