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The Planet enum example

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An example to make myself remember how powerful Java enums are!

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  1. public enum Planet {
  2.   MERCURY (3.303e+23, 2.4397e6),
  3.   VENUS   (4.869e+24, 6.0518e6),
  4.   EARTH   (5.976e+24, 6.37814e6),
  5.   MARS    (6.421e+23, 3.3972e6),
  6.   JUPITER (1.9e+27,   7.1492e7),
  7.   SATURN  (5.688e+26, 6.0268e7),
  8.   URANUS  (8.686e+25, 2.5559e7),
  9.   NEPTUNE (1.024e+26, 2.4746e7),
  10.   PLUTO   (1.27e+22,  1.137e6);
  11.  
  12.   private final double mass;   // in kilograms
  13.   private final double radius; // in meters
  14.   Planet(double mass, double radius) {
  15.       this.mass = mass;
  16.       this.radius = radius;
  17.   }
  18.   public double mass()   { return mass; }
  19.   public double radius() { return radius; }
  20.  
  21.   // universal gravitational constant  (m3 kg-1 s-2)
  22.   public static final double G = 6.67300E-11;
  23.  
  24.   public double surfaceGravity() {
  25.       return G * mass / (radius * radius);
  26.   }
  27.   public double surfaceWeight(double otherMass) {
  28.       return otherMass * surfaceGravity();
  29.   }
  30. }
  31.  
  32. // Example usage (slight modification of Sun's example):
  33. public static void main(String[] args) {
  34.     Planet pEarth = Planet.EARTH;
  35.     double earthRadius = pEarth.radius(); // Just threw it in to show usage
  36.  
  37.     // Argument passed in is earth Weight.  Calculate weight on each planet:
  38.     double earthWeight = Double.parseDouble(args[0]);
  39.     double mass = earthWeight/pEarth.surfaceGravity();
  40.     for (Planet p : Planet.values())
  41.        System.out.printf("Your weight on %s is %f%n",
  42.                          p, p.surfaceWeight(mass));
  43. }

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