Planet.java

// Enum type with data and behavior - Pages 149-150
package org.effectivejava.examples.chapter06.item30;

public enum Planet {
	MERCURY(3.302e+23, 2.439e6), VENUS(4.869e+24, 6.052e6), EARTH(5.975e+24,
			6.378e6), MARS(6.419e+23, 3.393e6), JUPITER(1.899e+27, 7.149e7), SATURN(
			5.685e+26, 6.027e7), URANUS(8.683e+25, 2.556e7), NEPTUNE(1.024e+26,
			2.477e7);
	private final double mass; // In kilograms
	private final double radius; // In meters
	private final double surfaceGravity; // In m / s^2

	// Universal gravitational constant in m^3 / kg s^2
	private static final double G = 6.67300E-11;

	// Constructor
	Planet(double mass, double radius) {
		this.mass = mass;
		this.radius = radius;
		surfaceGravity = G * mass / (radius * radius);
	}

	public double mass() {
		return mass;
	}

	public double radius() {
		return radius;
	}

	public double surfaceGravity() {
		return surfaceGravity;
	}

	public double surfaceWeight(double mass) {
		return mass * surfaceGravity; // F = ma
	}
}