使用自定义方法和构造函数创建枚举

public enum Planet {
/* from 
时 代 J a v a - N o w J a v a . c o m*/

    MERCURY(3.303e+23, 2.4397e6), VENUS(4.869e+24, 6.0518e6), EARTH(

            5.976e+24, 6.37814e6), MARS(6.421e+23, 3.3972e6), JUPITER(

            1.9e+27, 7.1492e7), SATURN(5.688e+26, 6.0268e7), URANUS(

            8.686e+25, 2.5559e7), NEPTUNE(1.024e+26, 2.4746e7);


    private final double mass; // in kilograms

    private final double radius; // in meters


    Planet(double mass, double radius) {

        this.mass = mass;

        this.radius = radius;

    }
    /** 
    来 自 
    时代Java
    **/


    private double mass() {

        return mass;

    }


    private double radius() {

        return radius;

    }


    // universal gravitational constant  (m3 kg-1 s-2)

    public static final double G = 6.67300E-11;


    double surfaceGravity() {

        return G * mass / (radius * radius);

    }


    double surfaceWeight(double otherMass) {

        return otherMass * surfaceGravity();

    }


    public static void main(String[] args) {

        if (args.length != 1) {

            System.err.println("Usage: java Planet <earth_weight>");

            System.exit(-1);

        }

        double earthWeight = Double.parseDouble(args[0]);

        double mass = earthWeight / EARTH.surfaceGravity();

        for (Planet p : Planet.values())

            System.out.printf("Your weight on %s is %f%n", p,

                    p.surfaceWeight(mass));

    }

}