/** reverse: given a String, reverse it */

public class reverse
{ /** Given String original, produce a new String in reverse order
    Note: to call reverse() from main(), I had to declare it static.
    This program does not construct any objects.
  */
  static String reverse(String original)
  { int len=original.length();    //length of original String
    StringBuffer copy=new StringBuffer(original); //copy the String
    //A String is immutable, so I copy it into a String so I can modify it.
    //Above statement creates a StringBuffer as a copy of original String
    
    int j=0;
    while(j < original.length()) //invariant: 0 < j < original.length
    { copy.setCharAt(j, original.charAt(len-j-1)); 
      //assign a char from original String into copy StringBuffer
      j++;  //increment
    }
    return copy.toString(); //convert StringBuffer back to String
  }
  
  /** test reverse: passing in "golf" should return "flog" */
  public static void main(String args[])
  { System.out.println("reverse of golf is " + reverse("golf") );
  }
}