File CountLetters.java contains a program that reads a word from the user and pr

Question

File CountLetters.java contains a program that reads a word from the user and prints the number of occurrences of each letter in the word. Save it to your directory and study it, then compile and run it to see how it works. In reading the code, note that the word is converted to all upper case first, then each letter is translated to a number in the range 0..25 (by subtracting 'A') for use as an index. No test is done to ensure that the characters are in fact letters.

1.     Run CountLetters and enter a phrase, that is, more than one word with spaces or other punctuation in between. It should throw an ArrayIndexOutOfBoundsException, because a non-letter will generate an index that is not between 0 and 25. It might be desirable to allow non-letter characters, but not count them. Of course, you could explicitly test the value of the character to see if it is between 'A' and 'Z'. However, an alternative is to go ahead and use the translated character as an index, and catch an ArrayIndexOutOfBoundsException if it occurs. Since you want don't want to do anything when a non-letter occurs, the handler will be empty. Modify this method to do this as follows:

Put the body of the first for loop in a try.

Add a catch that catches the exception, but don't do anything with it.

Compile and run your program.

2.     Now modify the body of the catch so that it prints a useful message (e.g., "Not a letter") followed by the exception. Compile and run the program. Although it's useful to print the exception for debugging, when you're trying to smoothly handle a condition that you don't consider erroneous you often don't want to. In your print statement, replace the exception with the character that created the out of bounds index. Run the program again; much nicer!

// ****************************************************************

// CountLetters.java

//

// Reads a words from the standard input and prints the number of

// occurrences of each letter in that word.

// ****************************************************************

import java.util.Scanner;

public class CountLetters

{

    public static void main(String[] args)

    {

      int[] counts = new int[26];

      Scanner scan = new Scanner(System.in);

      //get word from user

      System.out.print("Enter a single word (letters only, please): ");

      String word = scan.nextLine();

      //convert to all upper case

      word = word.toUpperCase();

      //count frequency of each letter in string

      for (int i=0; i < word.length(); i++)

          counts[word.charAt(i)-'A']++;

      //print frequencies

      System.out.println();

      for (int i=0; i < counts.length; i++)

          if (counts [i] != 0)

            System.out.println((char)(i +'A') + ": " + counts[i]);

    }

}

Explanation / Answer

1) import java.util.Scanner;
public class CountLetters
{
public static void main(String[] args)
{
int[] counts = new int[26];
Scanner scan = new Scanner(System.in);

//get word from user
System.out.print("Enter a single word (letters only, please): ");
String word = scan.nextLine();

//convert to all upper case
word = word.toUpperCase();

//count frequency of each letter in string
try{
for (int i=0; i < word.length(); i++)
counts[word.charAt(i)-'A']++;
}
catch(Exception e)
{
  
}

//print frequencies
System.out.println();
for (int i=0; i < counts.length; i++)
if (counts [i] != 0)
System.out.println((char)(i +'A') + ": " + counts[i]);
}

}

2)

import java.util.Scanner;
public class CountLetters
{
   public static void main(String[] args)
   {
       int[] counts = new int[26];
       Scanner scan = new Scanner(System.in);

       //get word from user
       System.out.print("Enter a single word (letters only, please): ");
       String word = scan.nextLine();

       //convert to all upper case
       word = word.toUpperCase();

       //count frequency of each letter in string
       for (int i=0; i < word.length(); i++)
       {
           if(word.charAt(i)>='A' && word.charAt(i)<='Z')
           {
               counts[word.charAt(i)-'A']++;
           }
           else
           {
               System.out.println("The character "+word.charAt(i)+" is not a letter.");
               System.out.println("Please enter only letters next time. See you!");
               return;
           }
       }

       //print frequencies
       System.out.println();
       for (int i=0; i < counts.length; i++)
           if (counts [i] != 0)
               System.out.println((char)(i +'A') + ": " + counts[i]);
   }

}

Related Questions

Navigate

• Browse (All)
• Browse F
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.