Permutations for digits represented by Phone Number

Given a telephone number print or produce all the possible telephone words or combinations of letters that can represent the given telephone number

public class WordsByPhoneNumberDigits {
 public static void main(String[] args) {
  String[] charsOnPhonedigits = { "", "", "abc", "def", "ghi", "jkl", "mno", "pqrs",
    "tuv", "wxyz" };
  String num = "23045";
  num = num.replace("0", "");
  num = num.replace("1", "");
  char[] target = new char[10];
  int bound = 0;
  decodeNumber(charsOnPhonedigits, num, target, bound);
 }

 private static void decodeNumber(String[] charsOnPhonedigits, String num,
   char[] target, int bound) {
  
  if (num.length() == 0) {// decoded the total string.no need of recursion
   StringBuilder str = new StringBuilder();
   for (int i = 0; i < bound; i++) {
    str.append(target[i]);
   }
   System.out.println(str);
   return;
  } else {
   int firstChar = Integer.parseInt(num.charAt(0) + "");
   int charsForDigit = charsOnPhonedigits[firstChar].length();
   String pattern = charsOnPhonedigits[firstChar];

   for (int k = 0; k < charsForDigit; k++) {
    target[bound] = pattern.charAt(k);
    if (num.length() != 1)
     decodeNumber(charsOnPhonedigits, num.substring(1), target,
       bound + 1);
    else
     decodeNumber(charsOnPhonedigits, "", target, bound + 1);
   }
  }
 }
}