@@ -0,0 +1,297 @@
+public class ChangeXY %7B%0A  public static void main (String... args) %7B%0A  // Result: yyyyyyhiyyyyyyyhi%0A    System.out.println(new ChangeXY ().changeXY (%22xxxxxxhixxxxxxxhi%22));%0A  %7D%0A  %0A  public String changeXY (String str) %7B%0A    return (str.indexOf (%22x%22)==-1)?str:changeXY(str.replace(%22x%22, %22y%22));%0A  %7D%0A%7D%0A

Create ChangeXY.java