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.

99% Battery available.

Conclusion:

1. Computer Class:

• The constructor is used to print  “Constructor of Computer class.” while creating a Computer object.
• The computer_method() is used to print  “Power gone! Shut down your PC soon.”.

2. Laptop Class:

• The constructor is used to print  “Constructor of Laptop class.” while creating a Laptop object.
• The laptop_method() is utilized to print “99% Battery available.”

3. Main Method:

• It creates instances of both Computer and Laptop classes.
• It calls computer_method() and laptop_method() on the respective instances for printing relevant messages.