java check if field is a number or letter

private static boolean getStringType(String str) {
	  String txt = str + "";
	  Pattern p = Pattern.compile("[0-9]*");
	  Matcher m = p.matcher(txt);
	  if (m.matches()) {// 输入的是数字
	  return true;
	  }
	  p = Pattern.compile("[a-zA-Z]");
	  m = p.matcher(txt);
	  return false;
   }