Demo - Number Utility

Number Utility Static Class

/**
  * Static Class to check format of a customer number 
  * Book Example modified by Kevin Roark 
  * */
public class NumberUtility {

	   /**
	    * The isValid method accepts a String as its argument 
	    * and tests its contents for a valid customer number.
	    */

	   public static boolean isValid(String custNumber)
	   {
	      boolean goodSoFar = true;  // Flag
	      int index = 0;             // Loop control variable

	      // Is the string the correct length?
	      if (custNumber.length() != 7)
	         goodSoFar = false;

	      // Test the first three characters for letters.
	      while (goodSoFar && index < 3)
	      {
	         if (!Character.isLetter(custNumber.charAt(index)))
	            goodSoFar = false;
	         index++;
	      }

	      // Test the last four characters for digits.
	      while (goodSoFar && index < 7)
	      {
	         if (!Character.isDigit(custNumber.charAt(index)))
	            goodSoFar = false;
	         index++;
	      }

	      // Return the results
	      return goodSoFar;
	   }
	   
	   public static void PrintHeader() 	   
	   {
		   System.out.println("*************************************");
		   System.out.println("     Number Utilty");
		   System.out.println("*************************************");
	   }

}

The NumberUtility class provides utility methods for checking the format of a customer number. Let's break it down step by step:

The class is declared as a public class named NumberUtility. It contains static methods and serves as a utility class.
The isValid method is a static method that accepts a String argument custNumber. It tests whether the given custNumber is a valid customer number.
Inside the isValid method, a boolean variable goodSoFar is initialized as true, acting as a flag to track the validity of the customer number. An integer variable index is also declared and initialized to 0, which will be used as a loop control variable.
The method checks the length of custNumber and if it is not equal to 7 characters, the goodSoFar flag is set to false.
The method then iterates through the first three characters of custNumber using a while loop. It checks if each character is a letter by calling the Character.isLetter method. If any character is not a letter, the goodSoFar flag is set to false.
After the loop completes, the method continues to iterate through the last four characters of custNumber using another while loop. It checks if each character is a digit by calling the Character.isDigit method. If any character is not a digit, the goodSoFar flag is set to false.
Finally, the isValid method returns the value of the goodSoFar flag, indicating whether the custNumber is a valid customer number or not.
The PrintHeader method is another static method that simply prints a header message to the console. It prints a series of asterisks and the title "Number Utility".

In summary, the NumberUtility class provides utility methods for checking the validity of a customer number and printing a header message. The isValid method checks if a given string meets the criteria of a valid customer number, while the PrintHeader method prints a header message to the console.

Driver

import java.util.Scanner;

/**
 * This program tests a customer number to determine
 * whether it is in the proper format.
 */

public class Demo2
{
   public static void main(String[] args)
   {
      String customer;  // To hold a customer number
      
      // Create a Scanner object for keyboard input.
      Scanner keyboard = new Scanner(System.in);
      
      //Print Program Header
      NumberUtility.PrintHeader();
      
      System.out.println("Enter a customer number in " +
                         "the form LLLNNNN");
      System.out.print("(LLL = letters and NNNN " +
                       "= numbers): ");

      // Get a customer number from the user.
      customer = keyboard.nextLine();
      
      // Determine whether it is valid.
      if (NumberUtility.isValid(customer))
      {
         System.out.println("That's a valid customer " +
                            "number.");
      }
      else
      {
         System.out.println("That is not the proper " +
                            "format.");
         System.out.println("Here is an example: " +
                            "ABC1234");
      }
      keyboard.close();
   }

}

The code tests a customer number entered by the user to determine whether it is in the proper format. Let's go through it step by step:

The code imports the Scanner class from the java.util package to facilitate keyboard input.
The Demo2 class is declared as a public class.
The main method starts. It declares a String variable customer to hold a customer number.
A Scanner object named keyboard is created to read input from the keyboard.
The NumberUtility.PrintHeader() method is called to print a program header message to the console. It is a static method from the NumberUtility class.
A prompt is displayed, asking the user to enter a customer number in the form "LLLNNNN" (where "LLL" represents letters and "NNNN" represents numbers).
The user is prompted to enter a customer number.
The entered customer number is stored in the customer variable using the keyboard.nextLine() method.
The NumberUtility.isValid(customer) method is called to determine whether the entered customer number is valid. It is a static method from the NumberUtility class.
If the customer number is valid, a message stating "That's a valid customer number." is printed to the console.
If the customer number is not valid, a message stating "That is not the proper format." is printed to the console, along with an example customer number "ABC1234".
The keyboard.close() statement closes the Scanner object.

In summary, the code prompts the user to enter a customer number, validates it using the NumberUtility.isValid method, and provides feedback about whether it is in the proper format. It also prints a program header message.