在已调用的构造函数的功能中禁用一些方法

Question

I've just finished my studies and I'm going to begin to apply. One of the things I'd like to have before applying is a kind of toolbox, full of dlls that I'll be able to use everywhere.

I'm actually dealing with a little problem, and don't really know what would be "best practice" for that.

I want the following class to be able to be used in plural ways. In my "Main", I want to be able to call some function in different ways :

MyDistance a = new MyDistance();
int b = a.Orthodrome(1.5 , 2.3, 5.8, 4.1);

And, I also want to be able to use it that way :

MyDistance a = new Distance(1.5 , 2.3, 5.8, 4.1);
int b = a.Orthodrome();
int c = a.Loxodrome();

The problem I have, is that in my "Main", I'm allowed to do this :

MyDistance a = new MyDistance();
int b = a.Orthodrome();

Which will always return an error.

He is a part of my class "MyDistance", I just give "for information", I don't know if it might be useful or not.

public class MyDistances
{
    private double _Lat1;
    private double _Long1;
    private double _Lat2;
    private double _Long2;

    /// <summary>
    /// Constructeur de la classe MyDistances. Il construit la classe avec les coordonnées géographiques de 2 points.
    /// </summary>
    /// <param name="lat1">Lattitude du premier point</param>
    /// <param name="long1">Longitude du premier point</param>
    /// <param name="lat2">Lattitude du second point</param>
    /// <param name="long2">Longitude du second point</param>
    public MyDistances(double lat1, double long1, double lat2, double long2)
    {
        this._Lat1 = (lat1 * Math.PI) / 180;
        this._Lat2 = (lat2 * Math.PI) / 180;
        this._Long1 = (long1 * Math.PI) / 180;
        this._Long2 = (long2 * Math.PI) / 180;
    }

    public MyDistances()
    {
        //Do nothing here.
    }

    /// <summary>
    /// Cette méthode retourne une distance exprimée en kilomètres, entre 2 points de l'espact
    /// </summary>
    /// <param name="lat1">La lattitude du premier point, exprimée en degrés</param>
    /// <param name="long1">La longitude du premier point, exprimées en degrés</param>
    /// <param name="lat2">La lattitude du second point, exprimée en degrés</param>
    /// <param name="long2">La longitude du second point, exprimée en degrés</param>
    /// <returns>Le typ</returns>
    public int Orthodrome(double lat1, double long1, double lat2, double long2)
    {
        this._Lat1 = (lat1 * Math.PI) / 180;
        this._Lat2 = (lat2 * Math.PI) / 180;
        this._Long1 = (long1 * Math.PI) / 180;
        this._Long2 = (long2 * Math.PI) / 180;

        return Orthodrome();
    }

    public int Orthodrome()
    {
        int distance = -1;
        try
        {
            distance = (int)Math.Round(2 * 6370 * Math.Asin(Math.Sqrt((Math.Sin((_Lat1 - _Lat2) / 2) * Math.Sin((_Lat1 - _Lat2) / 2) + Math.Cos(_Lat1) * Math.Cos(_Lat2) * Math.Sin((_Long1 - _Long2) / 2) * Math.Sin((_Long1 - _Long2) / 2)))));
        }
        catch (Exception)
        {
            throw;
        }
        return distance;
    }

}

What should I do to avoid being able to call the method without attributes, if the constructor that was called did not have any?

By the way, if you find anything else I'm doing wrong, do not hesitate to comment. I certainly still have a lot to learn.

Answer 1

You should make Orthodrome(double,double,double,double) static.

public static int Orthodrome(double lat1, double long1, double lat2, double long2)
{
    double Lat1 = (lat1 * Math.PI) / 180;
    double Lat2 = (lat2 * Math.PI) / 180;
    double Long1 = (long1 * Math.PI) / 180;
    double Long2 = (long2 * Math.PI) / 180;

    distance = CalculateOrthodrome(Lat1, Lat2, Long1, Long2);

    return distance;
}

Now in your main, you can do the following:

MyDistance.Orthodrome(2.3, 1.5, 2.8, 3.2);

You don't need to call MyDistance a = new MyDistance() in advance anymore. These kind of methods (functions) are called static (non-instance).

Edit: For your concern of copying code around:

private static int CalculateOrthodrome(double lat1, double long1, double lat2, double long2)
{
    return (int)Math.Round(2 * 6370 * Math.Asin(Math.Sqrt((Math.Sin((Lat1 - Lat2) / 2) * Math.Sin((Lat1 - Lat2) / 2) + Math.Cos(Lat1) * Math.Cos(Lat2) * Math.Sin((Long1 - Long2) / 2) * Math.Sin((Long1 - Long2) / 2)))));
}

Now use CalculateOrthodrome method for both instance and non instance methods.

Answer 2

只需将无参数构造函数设为私有：

private MyDistance() {}

Answer 3

You could set your fields to some default values so you can return at least some result if someone used your default constructor.

You could set a flag in your non-default constructor and check it in any parameterless methods. This would allow you to throw a clear exception.

In all fairness I would consider doing one method or the other, not both.