public class Triangle implements Polygon
{
    private double a;
    private double b;
    private double c;
    public Triangle(double a, double b, double c)
    {
        if(radicand(a, b, c) < 0)
        {
            throw new IllegalArgumentException();
        }
        this.a = a;
        this.b = b;
        this.c = c;
    }
    private static double radicand(double a, double b, double c)
    {
        double s = (a + b + c)/2.0;
        return s*(s - a)*(s - b)*(s - c);
    }
    public int numSides()
    {
        return 3;
    }
    public double area()
    {
        return Math.sqrt(radicand(a, b, c));
    }
    public double perimeter()
    {
        return a + b + c;
    }
    public double diameter()
    {
        return Math.max(Math.max(a,b),c);
    }
    public String toString()
    {
        return String.format("Triangle(%s, %s, %s)", a, b, c);
    }
}