Rectangle.java

public class Rectangle {
    public static final DEFAULT_EDGE_LENGTH = 1;
    public final double a;
    public final double b;
    public final double c;

    public Rectangle() {
        this(DEFAULT_EDGE_LENGTH, DEFAULT_EDGE_LENGTH, DEFAULT_EDGE_LENGTH);
    }

    public Rectangle(double a) {
        this(a, DEFAULT_EDGE_LENGTH, DEFAULT_EDGE_LENGTH);
    }

    public Rectangle(double a, double b) {
        this(a, b, DEFAULT_EDGE_LENGTH);
    }

    public Rectangle(double a, double b, double c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }

    public double volume() {
        return a * b * c;
    }

    public double area() {
        return 2 * (a * b + a * c + b * c);
    }

    public double edge() {
        return 4 * (a + b + c);
    }

    public static void main(String[] args) {
        double a = 2;
        double b = 3;
        double c = 4;

        Rectangle r1 = new Rectangle();
        assertEdges(r1, DEFAULT_EDGE_LENGTH, DEFAULT_EDGE_LENGTH, DEFAULT_EDGE_LENGTH);

        Rectangle r2 = new Rectangle(a);
        assertEdges(r1, a, DEFAULT_EDGE_LENGTH, DEFAULT_EDGE_LENGTH);

        Rectangle r3 = new Rectangle(a, b);
        assertEdges(r1, a, b, DEFAULT_EDGE_LENGTH);

        Rectangle r4 = new Rectangle(a, b, c);
        assertEdges(r1, a, b, c);

        assert r4.volume() == a * b * c;
        assert r4.area() == 2 * (a * b + a * c + b * c);
        assert r4.edge() == 4 * (a + b + c);
    }

    public static void assertEdges(Rectangle r, double a, double b, double c) {
        assert r.a == a && r.b == b && r.c == c;
    }
}