Implementation of 3D-Point usable for Multi-objective optimization

Point3.java

import static java.lang.String.format;

import java.util.Comparator;

/**
 * Sample implementation of a 3D double point.
 */
public final class Point3 implements Vec<Point3> {
    private final double _x;
    private final double _y;
    private final double _z;

    private Point3(final double x, final double y, final double z) {
        _x = x;
        _y = y;
        _z = z;
    }

    public double x() {
        return _x;
    }

    public double y() {
        return _y;
    }

    public double z() {
        return _z;
    }

    @Override
    public Point3 data() {
        return this;
    }

    @Override
    public int length() {
        return 3;
    }

    @Override
    public ElementComparator<Point3> comparator() {
        return Point3::cmp;
    }

    private static int cmp(final Point3 u, final Point3 v, final int i) {
        switch (i) {
            case 0: return Double.compare(u._x, v._x);
            case 1: return Double.compare(u._y, v._y);
            case 2: return Double.compare(u._z, v._z);
            default: throw new IllegalArgumentException("Illegal index: " + i);
        }
    }

    @Override
    public ElementDistance<Point3> distance() {
        return Point3::dst;
    }

    private static double dst(final Point3 u, final Point3 v, final int i) {
        switch (i) {
            case 0: return u._x - v._x;
            case 1: return u._y - v._y;
            case 2: return u._z - v._z;
            default: throw new IllegalArgumentException("Illegal index: " + i);
        }
    }

    @Override
    public Comparator<Point3> dominance() {
        return Point3::dom;
    }

    private static int dom(final Point3 u, final Point3 v) {
        return Pareto.dominance(u, v, 3, Point3::cmp);
    }

    @Override
    public int hashCode() {
        int hash = 37;
        hash += 31*Double.hashCode(_x) + 17;
        hash += 31*Double.hashCode(_y) + 17;
        hash += 31*Double.hashCode(_z) + 17;
        return hash;
    }

    @Override
    public boolean equals(final Object obj) {
        return obj == this ||
            obj instanceof Point3 &&
            Double.compare(((Point3) obj)._x, _x) == 0 &&
            Double.compare(((Point3) obj)._y, _y) == 0 &&
            Double.compare(((Point3) obj)._z, _z) == 0;
    }

    @Override
    public String toString() {
        return format("[%f, %f, %f]", _x, _y, _z);
    }

    public static Point3 of(final double x, final double y, final double z) {
        return new Point3(x, y, z);
    }
}