Question

Chapter 9 Lab
Text Processing and Wrapper Classes

Lab Objectives

• ? Use methods of the Character class and String class to process text

• ? Be able to use the StringTokenizer and StringBuffer classes

  Introduction

  In this lab we ask the user to enter a time in military time (24 hours). The program will convert and display the equivalent conventional time (12 hour with AM or PM) for each entry if it is a valid military time. An error message will be printed to the console if the entry is not a valid military time.

  Think about how you would convert any military time 00:00 to 23:59 into conventional time. Also think about what would be valid military times. To be a valid time, the data must have a specific form. First, it should have exactly 5 characters. Next, only digits are allowed in the first two and last two positions, and that a colon is always used in the middle position. Next, we need to ensure that we never have over 23 hours or 59 minutes. This will require us to separate the substrings containing the hours and minutes. When converting from military time to conventional time, we only have to worry about times that have hours greater than 12, and we do not need to do anything with the minutes at all. To convert, we will need to subtract 12, and put it back together with the colon and the minutes, and indicate that it is PM. Keep in mind that 00:00 in military time is 12:00 AM (midnight) and 12:00 in military time is 12:00 PM (noon).

  We will need to use a variety of Character class and String class methods to validate the data and separate it in order to process it. We will also use a Character class method to allow the user to continue the program if desired.

  The String Tokenizer class will allow us to process a text file in order to decode a secret message. We will use the first letter of every 5th token read in from a file to reveal the secret message.

  Task #1 Character and String Class Methods

1. Copy the files Time.java (code listing 9.1) and TimeDemo.java (code listing 9.2) from the StudentCD or as directed by your instructor.

2. In the Time.java file, add conditions to the decision structure which validates the data. Conditions are needed that will

   1. Check the length of the string

   2. Check the position of the colon

   3. Check that all other characters are digits

48

Answer 1

Task #1 Character and String Class Methods:

Sample Output:

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Complete Program:

// File: Time.java
/**Represents time in hours and minutes using the customary conventions*/
public class Time
{
/**hours in conventional time*/
private int hours;

/**minutes in conventional time*/
private int minutes;

/**true if afternoon time, false if morning time*/
private boolean afternoon;

/**Constructs a cutomary time (12 hours, am or pm) from a military time ##:##
@ param militaryTime time in the military format ##:##*/
public Time(String militaryTime)
{
  //Check to make sure something was entered
  if(militaryTime == null)
  {
   System.out.println("You must enter a valid miliary time.");
  }
  //Check to make sure there are 5 characters
  else if(militaryTime.length() != 5)
  {
   System.out.println(militaryTime + " is not a valid miliary time.");
  }
  else
  {
   //Check to make sure the colon is in the correct spot
   if(militaryTime.charAt(2) != ':')
   {
    System.out.println(militaryTime + " is not a valid miliary time.");
   }
   //Check to make sure all other characters are digits
   else if(!Character.isDigit(militaryTime.charAt(0)))
   {
    System.out.println(militaryTime + " is not a valid miliary time.");
   }
   else if(!Character.isDigit(militaryTime.charAt(1)))
   {
    System.out.println(militaryTime + " is not a valid miliary time.");
   }
   else if(!Character.isDigit(militaryTime.charAt(3)))
   {
    System.out.println(militaryTime + " is not a valid miliary time.");
   }
   else if(!Character.isDigit(militaryTime.charAt(4)))
   {
    System.out.println(militaryTime + " is not a valid miliary time.");
   }
   else
   {
    //SEPARATE THE STRING INTO THE HOURS
    //AND THE MINUTES, CONVERTING THEM TO
    //INTEGERS AND STORING INTO THE
    //INSTANCE VARIABLES
    hours = Integer.parseInt( militaryTime.substring(0, 2));
    minutes = Integer.parseInt(militaryTime.substring(3, 5));
    
    //validate hours and minutes are valid values
    if(hours > 23)
    {
     System.out.println(militaryTime + " is not a valid miliary time.");
    }
    else if(minutes > 59)
    {
     System.out.println(militaryTime + " is not a valid miliary time." );
    }
    //convert military time to conventional time
    //for afternoon times
    else if(hours > 12)
    {
     hours = hours - 12;
     afternoon = true;
     System.out.println(this.toString());
    }
    //account for midnight
    else if(hours == 0)
    {
     hours = 12;
     System.out.println(this.toString());
    }
    //account for noon
    else if(hours == 12)
    {
     afternoon = true;
     System.out.println(this.toString());
    }
    //morning times don't need converting
    else
    {
     System.out.println(this.toString());
    }
   }
  }
}

/**toString method returns a conventional time
* @return a conventional time with am or pm*/
public String toString()
{
  String am_pm;
  String zero = "";
  
  if(afternoon)
   am_pm = "PM";
  else
   am_pm = "AM";
  
  if(minutes < 10)
   zero = "0";
  
  return hours + ":" + zero + minutes + " " + am_pm;
}
}

-------------------------------------------------------------------------------------------

// File: TimeDemo.java
import java.util.Scanner;
public class TimeDemo
{
public static void main (String [] args)
{
  Scanner keyboard = new Scanner(System.in);
  char answer = 'Y';
  
  String enteredTime;
  String response;

  while(Character.toUpperCase(answer)=='Y')
  {
   System.out.print("Enter a miitary time using the ##:## form ");
   enteredTime = keyboard.nextLine();
   
   Time now = new Time(enteredTime);
   
   System.out.print("\nDo you want to enter another (Y/N)? ");
   response = keyboard.nextLine();
   answer = response.charAt(0);
  }
}
}

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Task #2 StringTokenizer and StringBuffer classes:

Sample Output:

-------------------------------------------------------------------------------------------------------------------------------------

Complete Program:

// File: SecretFileDemo.java
import java.io.*;
import java.util.*;
public class SecretFileDemo
{
public static void main(String[] args)
{
  try
  {
   Scanner infile = new Scanner(new File("secret.txt"));
   StringBuffer sb = new StringBuffer();
   StringTokenizer tokens;
   
   String line;
   String word;
   char firstChar;
   int count = 0;   
        
   while(infile.hasNextLine())
   {
    line = infile.nextLine();
    
    tokens = new StringTokenizer(line);
    
    while(tokens.hasMoreTokens())
    {
     word = tokens.nextToken();
     count++;
     
     if(count % 5 == 0)
     {
      firstChar = Character.toUpperCase(word.charAt(0));
      
      sb.append(firstChar);
     }
      
    }
   }
   
   System.out.println("Secre word: " + sb);
  }
  catch(FileNotFoundException e)
  {
   System.out.println("Input file is not opened.");
   System.exit(0);
  }
}
}