public void slide(){
  int position=0;
  if (items != null) {
    position=items.size() / 2;
  }
  slide(position);
}

public void slide ( ) { int position = 0 ; if ( items != null ) { position = items . size ( ) / 2 ; } slide ( position ) ; }
slide the panel depending on the current state . if slide up , the position is the half of the elements .
