//
// Exceptional String Cleaning :)
//

public class cleanString {

  public static String toString(String source) throws 
	 IllegalCharactersException,
	 FirstLetterNotCapitalizedException,
	 SentenceNotPeriodTerminatedException {

    int i, len = source.length();
    StringBuffer dest = new StringBuffer(len);

    if (!isCapitalLetter(source.charAt(0))) {
      throw new FirstLetterNotCapitalizedException("First letter of sentence not capitalized.");
    }

    if (source.charAt(source.length()-1) != '.') {
      throw new SentenceNotPeriodTerminatedException("Sentence not period terminated.");
    }

    for (i = 0; i < (len-1); i++ ) {	// all but the trailing "."
      if (isLegal(source.charAt(i))) {
        dest.append(cleanLetter(source.charAt(i)));
      }
      else {
	throw new IllegalCharactersException("Illegal character in sentence");
      }
    }
    return dest.toString();
  }

  static boolean isLegal(char letter) {

    //
    // Definition of a legal char:
    //
    //  - Upper/lower A-Z
    //  - blank
    // 

    if (letter >= 'a' && letter <= 'z') return true;
    if (letter >= 'A' && letter <= 'Z') return true;
    if (letter == ' ') return true;
    return false;
  }

  static char cleanLetter(char letter) {
    if (letter >= 'A' && letter <= 'Z') return ((char) ((letter - 'A') + 'a'));
    return(letter);
  }

  static boolean isCapitalLetter(char letter) {
    if (letter >= 'A' && letter <= 'Z') return true;
    return false;
  }

}