public String moveBack(){
  Check.isTrue(currentIndex > 0,"currentIndex > 0");
  currentIndex--;
  return history.get(currentIndex);
}

public String moveBack ( ) { Check . isTrue ( currentIndex > 0 , "currentIndex > 0" ) ; currentIndex -- ; return history . get ( currentIndex ) ; }
return the previous url in the list ( relative to the current position ) and moves the index back to make this the now current position .
