Exam & Solution - A Concise and Practical Introduction to Programming Algorithms in Java - page 231

- Write a static function boolean bump(Atom a, Atom b) that takes as
arguments two atoms a and b , and return true if and only if the
distance between their centers is strictly less than the sum of their
radii (this will represent a collision between two atoms). This function
shall be defined inside the class Atom .

SOLUTION:

Program 11.2 Class Atom with the bump predicate
public class Atom

{

Point3D center ;

double radius ;
public static final double H RADIUS = 1 . 2 ;
public static final double O RADIUS = 1 . 5 ;
public Atom ( double x, double y, double z, double rad
) {
this .center= new Point3D (x , y , z ) ;
this .radius=rad;
public static boolean bump ( Atom a , Atom b )

{

return Point3D . distance (a. center , b. center )

< a. radius + b. radius ;
}
}

// Temporary class; Shall be enhanced next

- Write a class Molecule that allows us to define a 3D molecule as an
array of atoms, and provide the class with a constructor that takes as
argument a reference to this array.

SOLUTION:

Program 11.3 Class Molecule
public class Molecule

{

Atom [ ] atoms ;
public Molecule ( Atom [] t) {

this . atoms = t ;
}
}

- Using a new class Test , write a program that builds a water molecule
H20 with its oxygen atom located at (0 , 0 . 4 , 0) and the two hydrogen
atoms located at (0 . 76 , − 0 . 19 , 0) and ( − 0 . 76 , − 0 . 19 , 0) (units still

being angstrom).