String Pair Swapping Loop

Consider the following transform method.

public static String transform(String str) {
  String transformed = "";
  for (int i = 0; i < str.length() - 1; i += 2) {
    transformed += str.substring(i + 1, i + 2) + str.substring(i, i + 1);
  }
  if (str.length() % 2 != 0) {
    transformed += str.substring(str.length() - 1);
  }
  return transformed;
}

What is returned by the call transform("1234567")?