Caesar Cipher Command Line Decrypter

CaesarCipher.java

public class CaesarCipher {

	public static void main(String args[]){
		
		if (args.length == 3)
		{
			//output decrypted string
			System.out.println(decryptString(args[0], args[1], args[2]));
		}
		else
		{
			// show usage message
			System.out.println("usage: java CaesarCipher <encrypted answer> <decrypted answer> <encrypted string>");
		}
		
	} // end main
	
	private static String decryptString(String encryptedAnswer, String decryptedAnswer, String encryptedString )
	{
		char[] letters = { 'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z' };
		
		// calculate difference between letters
		char enfirst = encryptedAnswer.toLowerCase().charAt(0);
		char defirst = decryptedAnswer.toLowerCase().charAt(0);

		// cast to int
		int e = (int) enfirst;
		int d = (int) defirst;

		// get difference between the 2 letters
		int diff = d - e;
	
		StringBuffer decryptedString = new StringBuffer();
		
		// decrypt string		
		for (int i = 0; i < encryptedString.length(); i++)
		{
			// get current char
			char curChar = encryptedString.charAt(i);

			if (curChar != ' ' && curChar != ',' && curChar != '-')
			{
				// get number of current char
				int curCharInt = (int) curChar;
				
				// get position of decrypted char
				int posOfCharInLettersArray = ((curCharInt - 97 + diff) % letters.length + letters.length) % letters.length;
				
				// get decrypted char
				char newChar = letters[posOfCharInLettersArray];

				// build output string
				decryptedString.append(newChar);
			}
			else 
			{
				// build output string
				decryptedString.append(curChar);
			}
		}
		
		return decryptedString.toString();
	} // end decryptString 
		
} // end class