private static void swap(Object[] x,int a,int b){
  Object t=x[a];
  x[a]=x[b];
  x[b]=t;
}

private static void swap ( Object [ ] x , int a , int b ) { Object t = x [ a ] ; x [ a ] = x [ b ] ; x [ b ] = t ; }
swaps x [ a ] with x [ b ] .
