Re: Declaring members for Interfaces

Todd <>
Tue, 29 Apr 2008 11:22:47 -0700 (PDT)

This example is from the Sun Tutorial site:

public enum Planet {
    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;
    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) {
        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));


Since the members of the enumeration (mass, radius)
are directly accessible without getters, even though
private, what use is the private keyword?

I had thought that private worked in an enum as it
does in all other classes, hence my previous question.
Only after some compiling and playing with these examples
did I find that private was meaningless in the enum.
Further, I can change the value of any non-final member
without an accessor. To me, it seems that enums are
rather loose.

My test included the following lines and changed mass to
non-final, but left it private:

System.out.println( Planet.EARTH.mass );
Planet.EARTH.mass = 12;
System.out.println( Planet.EARTH.mass );


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