Exceptions That Are Not Errors
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 C:\TEMP 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
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 catch 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 like "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.
