Weekly Lab 7 Exceptions Aren't Always Errors
Maximum Points = 10
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:
2.
// ****************************************************************
// 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]);
}
}
(Due before end of the day on Friday, February 24, 2011) Submit your .java files containing your program to the dropbox in WebCT.
Grades are determined using the following scale: