Creating "Main.java":

• Create a class named "Main".
  • Define the "main ()" method.
    • Declare required variables.
    • Do till the user enters "n" using "while" condition.
      • Get the string from the user.
      • Check if the length of the string is greater than or equal to 20.
        • Create an object "e" for the class. Here the exception is thrown using default constructor.
        • Get and print the message using the method "e.getMessage()".
      • Else,
        • Print the number of characters.
      • Ask whether the user wants to continue or not and store the response in a variable "response".
      • Check if the response is equal to "n".
        • Break the loop.

Creating "MessageTooLongException.java":

• Create a class named "MessageTooLongException" that extends "Exception".
  • Define a default constructor that calls the parent class’s method using "super ()" by passing a message.
  • Define a parameterized constructor that calls the parent class’s method using "super ()" by passing a message that is given as the argument.

Program:

MessageTooLongException.java:

//Define a class

public class MessageTooLongException extends Exception

{

//Default constructor

public MessageTooLongException()

{

//Call the parent class by passing the message

super("Message Too Long!");

}

//Parameterized constructor

public MessageTooLongException(String message)

{

//Call the parent class by passing the message

super(message);

}

}

Main.java:

//import the package

import java.util.Scanner;

//Main class

class Main

{

//Define main method

public static void main(String[] args)

{

//Create an object for the scanner class

Scanner sc = new Scanner(System.in);

//Declare required variables

String str, response = "y";

//Do till the user enters 'n'

while(response...