【说明】一条直线是由两个点组成的，代码如下。
public class Point
{
private int x, y; //coordinate
public Point (int x, int y)
{ (1) =x; (2) ;}
public int GetX()
{ return x; }
public int GetY()
{ return y; }
}
class Line //line segment
{
private (3) ; //extremc points
Line (Point a, Point b) //constructor
{ p1 = (4) ;
p2= (5) ;
}
public double Length() {
return Math.sqrt (Math.pow (p2.GetX()-pl.GetX(),2)
+Math.pow (p2.GetY()-p1.GetY(),2)) ;
}
}