@@ -0,0 +1,219 @@
+public String altPairs(String str) %7B%0A  String out = %22%22;%0A  for (int i=0; i%3Cstr.length(); i+= 4)%0A    if (i==str.length()-1)%0A      out += str.substring(i, i+1);%0A    else%0A      out += str.substring(i, i+2);%0A  return out;%0A%7D%0A

Update and rename stringX.java to altPairs.java