public static void main(String[] args) {
    MyString ms = new MyString("abc def");
    System.out.println(ms.reverse()); // fed cba
  }
}

class MyString {

  String wrapped;

  MyString(String s) {
    wrapped = s;
  }

  public String toString() {
    return wrapped;
  }

  MyString reverse() {
    StringBuilder sb = new StringBuilder(wrapped);
    return new MyString(sb.reverse().toString());

  }
}