ZysCube

public class ZysCube {

    private double lengthOfSide;
    private double density;

    public ZysCube(double lengthOfSide, double density) {
        this.lengthOfSide = Math.max(lengthOfSide, 0.0);
        this.density = Math.max(density, 0.0);
    }

    public double getCubeArea() {
        return 6 * Math.pow(this.lengthOfSide, 2);
    }

    public double getCubeMass() {
        return Math.pow(this.lengthOfSide, 3) * this.density;
    }
}