不同子类的相同方法

Question

I have a C# -Class Point with two Subclasses ColorPoint and AmountPoint .

Point-Class

public class Point
{
    double x; // Position x
    double y; // Position y

    public Point(double pos_x, double pos_y) // Constructor
    {
        this.x = pos_x;
        this.y = pos_y;
    }
}

public class ColorPoint : Point
{
    double color; // White value (0 to 255)
}

public class AmountPoint : Point
{
    int amount; // Amount of Persons standing at this point
}

Now I want two things.

1. I want to have a method AdaptMeshPoints that accepts both ColorPoint and AmountPoint input-lists and I can change the common parameters of both (which are the parameters in Point )

2. I want to tell the method AdaptMeshPoints , which parameter of the Subclass it should print out.

This should than look something like this:

public class main
{
    public main()
    {
        List<ColorPoint> colorList = new List<ColorPoint>(4);
        AdaptMeshPoints<ColorPoint>(colorList, color);
    }

    public List<var> AdaptMeshPoints<var>(List<var> pointList, varType whatToPrint)
    {
        pointList[0].x = 45;
        Console.WriteLine(pointList[0].whatToPrint);
    }
}

Answer 1

I'm assuming this is C# from the text in your question, even though your question is tagged with both C# and Java.

To be able to set pointList[0].x , you need to tell the compiler that T will always be a Point (or something which inherits from it). Do this with a generic type constraint ( where T : Point ).

You can also pass a delegate which describes which property you want to print:

public main()
{
    List<ColorPoint> colorList = new List<ColorPoint>(4);
    AdaptMeshPoints(colorList, x => x.color.ToString());
}

public List<T> AdaptMeshPoints<T>(List<T> pointList, Func<T, string> whatToPrint)
    where T : Point
{
    pointList[0].x = 45;
    Console.WriteLine(whatToPrint(pointList[0]));
}

Answer 2

To 1. Make a function that takes Point[]. Casting is automatically done if there is "no danger of Data loss" and such polymorphy cases are where this applies.

(I am not 100% certain if this is Polymorphy or falls more into the area of co- and Contra-variance. However the rules here are intentionally very similar).

To 2. This can be solved at least by:

• A extra parameter and a switch/case block
• Handing the function anotehr function or interface that holds the actuall code to access the variable
• Hand the code a Lambda or anonymous function to do the actuall work.

So you got to "pick your Posion".