Java to Capitalize the First Letter of Each Word in a Sentence

Every once in a while, I find myself stuck on the most mundane and boring coding problems.  Take this one, for example: use Java to capitalize the first letter of each word in a sentence.  Amazingly, I actually had a need today to write some Java code that does just that.  Sounds trivial; I actually ended up spending almost half-an-hour on this (I know, you can laugh at me, but I just couldn't wrap my head around this one).  My first reaction was to use a regular expression, but I realized that, unlike Perl, Java doesn't support \u which can come in handy when capitalizing letters in a regex.  From what I read online, there are quite a few back references and other escape sequences built into Perl regular expressions that Java doesn't support.

I finally bit the bullet, and solved this the introduction-to-programming way, which is to loop through each character in the String, and capitalize the letters that sit at the start of a word-boundary.  It makes me shudder when I have to "loop through" letters in a String, but I guess there are some problems that simply cannot be solved without doing just that.

Here's the code:

public static String capitalizeFirstLetters ( String s ) {

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

        if (i == 0) {
            // Capitalize the first letter of the string.
            s = String.format( "%s%s",
                         Character.toUpperCase(s.charAt(0)),
                         s.substring(1) );
        }

        // Is this character a non-letter or non-digit?  If so
        // then this is probably a word boundary so let's capitalize
        // the next character in the sequence.
        if (!Character.isLetterOrDigit(s.charAt(i))) {
            if (i + 1 < s.length()) {
                s = String.format( "%s%s%s",
                             s.subSequence(0, i+1),
                             Character.toUpperCase(s.charAt(i + 1)),
                             s.substring(i+2) );
            }
        }

    }

    return s;

}

Note that another solution might involve using a StringTokenizer, like so:

public static String capitalizeFirstLettersTokenizer ( String s ) {
        
    final StringTokenizer st = new StringTokenizer( s, " ", true );
    final StringBuilder sb = new StringBuilder();
     
    while ( st.hasMoreTokens() ) {
        String token = st.nextToken();
        token = String.format( "%s%s",
                                Character.toUpperCase(token.charAt(0)),
                                token.substring(1) );
        sb.append( token );
    }
        
    return sb.toString();
                
}

Or, you could avoid writing custom code all together and use something like org.apache.commons.lang.WordUtils.capitalize().

Enjoy.