• Author: Graham Mitchell
• Filename: LetterAtATime.java

Letter at a Time

Did you know that using a loop, you can examine a String one letter at a time? The two key built-in String methods are length() and charAt().

• length() returns an int representing the total number of characters in the String (including punctuation and whitespace). For example, if the variable str contains the String "hello", then str.length() will return 5.
• charAt( int n ) returns the n^th character (char) in the String. The character positions are zero-based, so if the variable str contains the String "ligature", then str.charAt(0) will return 'l', and str.charAt(4) will return 't'.

Files Needed

• LetterAtATime.java

(Do not re-type this program. Simply download a copy of the file by right-clicking and choosing "Save link as..." from the context menu. Save it into your normal code folder.)

What You Should See

What is your message? A man, a plan, a canal: Panama!

Your message is 31 characters long.
The first character is at position 0 and is 'A'.
The last character is at position 30 and is '!'.

Here are all the characters, one at a time:

	0 - 'A'
	1 - ' '
	2 - 'm'
	3 - 'a'
	4 - 'n'
	5 - ','
	6 - ' '
	7 - 'a'
	8 - ' '
	9 - 'p'
	10 - 'l'
	11 - 'a'
	12 - 'n'
	13 - ','
	14 - ' '
	15 - 'a'
	16 - ' '
	17 - 'c'
	18 - 'a'
	19 - 'n'
	20 - 'a'
	21 - 'l'
	22 - ':'
	23 - ' '
	24 - 'P'
	25 - 'a'
	26 - 'n'
	27 - 'a'
	28 - 'm'
	29 - 'a'
	30 - '!'

Your message contains the letter 'a' 10 times. Isn't that interesting?

Study Drills

Assignments turned in without these things will receive half credit or less.

1. The for loop is defined so that it repeats as long as i < message.length(). Try changing it to <=. What happens? Answer in a comment, then change it back.
2. If a string variable contains the value "box", what is its length()? What is the position of the last character (the 'x')?
3. So, why does the for loop repeat as long as i < message.length() instead of i <= message.length()?
4. Currently the code prints out the number of 'a's in the message. Change it so that it prints out the number of vowels (a A e E i I o O u U).

©2013–2015 Graham Mitchell

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