Exam & Solution - A Concise and Practical Introduction to Programming Algorithms in Java - page 230

- Give a static function Point3D add(Point3D p, Point3D q) that takes as
arguments two points p and q , and return a new point equal to p + q .
This function shall be inserted inside class Point3D .

- Give a static function void scale(Point3D p, double k) that multiplies
the coordinates of point p by scalar number k .Thatis, p becomes k.p .
This function shall be located inside class Point3D as well.

SOLUTION:

Program 11.1 The class Point3D
public class Point3D {

double x, y, z;
public Point3D ( double x0 , double y0 , double z0) {

this .x = x0;
this .y = y0;
this .z = z0;
static double sqr ( double x)

}
public static double distance ( Point3D p, Point3D q)
{
return Math . sqrt (sqr (q.x

{ return x ∗ x;

− p.x) + sqr (q.y − p.y)

+sqr(q.z − p.z));
} public static Point3D add ( Point3D p , Point3D q) {
return new Point3D (p.x + q.x, p.y + q.y, p.z + q.z);
} public static void scale ( Point3D p, double k)

{

p.x ∗ =k;
p.y ∗ =k;
p.z ∗ =k;
}
}

- Give a class Atom that allows us to define atoms with two object
fields:

- center of type Point3D denoting the location ( x, y, z ) of the center of
this atom, and

- radius of type double that encodes the radius of this atom.

Provide a constructor Atom( double x, double y, double z, double
rad) to this class that initialize objects of this type.

Further, add to this class two constants H RADIUS = 1.2 and
O RADIUS = 1.5 that represent the radii in angstrom for the hydrogen
and oxygen atoms, respectively.