question: public double distance ( Point2D pt ) { final double x_distance = ( pt . getX ( ) - x ) * ( pt . getX ( ) - x ) ; final double y_distance = ( pt . getY ( ) - y ) * ( pt . getY ( ) - y ) ; return Math . sqrt ( x_distance + y_distance ) ; }
target:  Returns the Euclidean distance between a specified point and this point.