char[] alphabet = new char[] {'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'};
	  char[] numbers = new char[] {'0','1','2','3','4','5','6','7','8','9'};
	  char[] charArray = str.toCharArray();
	  String valid = "";

	  for (int i = 0; i < charArray.length; i++)
	  {
		  for (int j = 0; j < alphabet.length; j++)
		  {
			  for (int k = 0; k < numbers.length; k++)
			  {
				  if (charArray[i] == alphabet[j] || charArray[i] == numbers[k])
				  {
					  try
					  {
						  if (charArray[i-1] == '+' && charArray[i+1] == '+')
						  {
							  valid = "true";
						  }
					  }
					  catch (Exception e)
					  {
						  return "false";
					  }
				  }
			  }
		  }
	  }

    return valid;