Initializing a property in c#

Question

I have a constructor I am trying to build with the header public KsuPoint(double x0, double y0)

now i also have properties in the class as shown below

private double x;

    public double X
    {
        get { return x; }

    }

    private double y;

    public double Y
    {
        get { return y; }

    }

This constructor is suppose to initialize the properties X and Y ...

is this correct? or am i off?

public KsuPoint(double x0, double y0)
    {
        new KsuPoint(x0, y0);
    }

Answer 1

The constructor needs to map it's parameters to the private fields of the class - here is what your class should look like:

class KsuPoint
{
    private double x;
    private double y;

    public double X { get { return x; } }
    public double Y { get { return y; } }

    public KsuPoint(double x0, double y0)
    {
        this.x = x0;
        this.y = y0;
    }
}

If you want to be more concise you could do this:

class KsuPoint
{
    public double X { get; private set; }
    public double Y { get; private set; }

    public KsuPoint(double x0, double y0)
    {
        this.X = x0;
        this.Y = y0;
    }
}

Answer 2

No you only use new when you want to create a new object of the class typically outside the class.

public KsuPoint(double x0, double y0)
{
    x = x0;
    y = y0;
}

Somewhere else in your code you would have:

KsuPoint point = new KsuPoint(3, 4);

If you are using C# 3.0 you can also do this:

class KsuPoint
{
    public double X { get; private set; }
    public double Y { get; private set; }

    public KsuPoint(double x0, double y0)
    {
        X = x0;
        Y = y0;
    }
}

Answer 3

No, that would result in a bad case of infinite recursion. Just assign the values normally, i.e.

x = x0;
y = y0;

Answer 4

You need to add setters, like this:

public double X
{
    get { return x; }
    set { x = value; }
}

If you just want simple getters and setters, this syntax is shorter, and easier to read in my opinion:

public double x0 { get; set; }
public double y0 { get; set; }

Then you simply assign the parameter to the field, like many of the other answers show.

Answer 5

Another variant would be:

class KsuPoint 
{ 
    readonly double x; 
    readonly double y; 

    public double X { get { return x; } } 
    public double Y { get { return y; } } 

    public KsuPoint(double x0, double y0) 
    { 
        this.x = x0; 
        this.y = y0; 
    } 
}

This makes instances of KsuPoint truely immutable; when using a private setter, member functions can still make changes.

At this point, you could also drop the properties and just expose the fields directly (although properties are generally a good idea):

class KsuPoint 
{ 
    public readonly double X; 
    public readonly double Y; 

    public KsuPoint(double x0, double y0) 
    { 
        this.X = x0; 
        this.Y = y0; 
    } 
}

Finally, this isn't what you showed in your sample--and only works for C# 3.0: if the default values of X and Y are satisfactory, you could drop the constructor and write

class KsuPoint 
{         
    public double X { get; set; }
    public double Y { get; set; }
}
var ksuPoint = new KsuPoint() { X=3.1, Y=41.59 };