Lære Udfordring: Polymorfi

Programmet nedenfor indeholder en superklasse kaldet Shape og tre afledte klasser kaldet Rectangle, Square og Circle. Problemet med koden er, at metoderne ikke er korrekt overskrevet, da output viser 0.0 for alle tre Console.WriteLine-udtryk, hvilket antyder, at metoderne fra basisklassen bliver udført i stedet for metoderne fra de afledte klasser.

Rediger koden, så de to metoder, nemlig getArea og calculatePerimeter, bliver korrekt overskrevet.

index.cs


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using System;
using System.Collections.Generic;

class Shape
{
    // Perimeter is the length of the 'outline' of a shape
    public float perimeter;

    // Change code below this line
    public float getArea()
    {
        return 0.0f;
    }

    protected float calculatePerimeter()
    {
        return 0.0f;
    }
    // Change code above this line
}

class Rectangle : Shape
{
    float width;
    float height;

    public Rectangle(float width, float height)
    {
        this.width = width;
        this.height = height;
        this.perimeter = this.calculatePerimeter();
    }

    // Change code below this line
    public float getArea()
    {
        return width * height;
    }

    protected float calculatePerimeter()
    {
        return width * 2 + height * 2;
    }
    // Change code above this line
}

class Square : Shape
{
    float length;

    public Square(float length)
    {
        this.length = length * length;
        this.perimeter = calculatePerimeter();
    }

    // Change code below this line
    public float getArea()
    {
        return length * length;
    }

    protected float calculatePerimeter()
    {
        return 4 * length;
    }
    // Change code above this line
}

class Circle : Shape
{
    float radius;

    public Circle(float radius)
    {
        this.radius = radius;
        this.perimeter = calculatePerimeter();
    }

    // Change code below this line
    public float getArea()
    {
        return 3.14f * radius * radius;
    }

    protected float calculatePerimeter()
    {
        return 2.00f * 3.14f * radius;
    }
    // Change code above this line
}

class ConsoleApp
{
    static void Main()
    {
        List<Shape> shapes = new List<Shape>();
        shapes.Add(new Rectangle(10f, 20f));
        shapes.Add(new Square(10f));
        shapes.Add(new Circle(10f));

        foreach (Shape shape in shapes)
        {
            Console.WriteLine(shape.getArea());
        }
    }
}

Brug virtual-nøgleordet i basisklassen for at gøre metoderne overskrivelige.
Tilføj override-nøgleordet i metode-definitionerne i hver afledt klasse.

index.cs


              123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107
            
using System;
using System.Collections.Generic;

class Shape
{
    // Perimeter is the length of the 'outline' of a shape
    public float perimeter;

    // Change code below this line
    public virtual float getArea()
    {
        return 0.0f;
    }

    protected virtual float calculatePerimeter()
    {
        return 0.0f;
    }
    // Change code above this line
}

class Rectangle : Shape
{
    float width;
    float height;

    public Rectangle(float width, float height)
    {
        this.width = width;
        this.height = height;
        this.perimeter = this.calculatePerimeter();
    }

    // Change code below this line
    public override float getArea()
    {
        return width * height;
    }

    protected override float calculatePerimeter()
    {
        return width * 2 + height * 2;
    }
    // Change code above this line
}

class Square : Shape
{
    float length;

    public Square(float length)
    {
        this.length = length * length;
        this.perimeter = calculatePerimeter();
    }

    // Change code below this line
    public override float getArea()
    {
        return length * length;
    }

    protected override float calculatePerimeter()
    {
        return 4 * length;
    }
    // Change code above this line
}

class Circle : Shape
{
    float radius;

    public Circle(float radius)
    {
        this.radius = radius;
        this.perimeter = calculatePerimeter();
    }

    // Change code below this line
    public override float getArea()
    {
        return 3.14f * radius * radius;
    }

    protected override float calculatePerimeter()
    {
        return 2.00f * 3.14f * radius;
    }
    // Change code above this line
}

class ConsoleApp
{
    static void Main()
    {
        List<Shape> shapes = new List<Shape>();
        shapes.Add(new Rectangle(10f, 20f));
        shapes.Add(new Square(10f));
        shapes.Add(new Circle(10f));

        foreach (Shape shape in shapes)
        {
            Console.WriteLine(shape.getArea());
        }
    }
}

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Sektion 5. Kapitel 5

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Rediger koden, så de to metoder, nemlig getArea og calculatePerimeter, bliver korrekt overskrevet.

index.cs


              123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107
            
using System;
using System.Collections.Generic;

class Shape
{
    // Perimeter is the length of the 'outline' of a shape
    public float perimeter;

    // Change code below this line
    public float getArea()
    {
        return 0.0f;
    }

    protected float calculatePerimeter()
    {
        return 0.0f;
    }
    // Change code above this line
}

class Rectangle : Shape
{
    float width;
    float height;

    public Rectangle(float width, float height)
    {
        this.width = width;
        this.height = height;
        this.perimeter = this.calculatePerimeter();
    }

    // Change code below this line
    public float getArea()
    {
        return width * height;
    }

    protected float calculatePerimeter()
    {
        return width * 2 + height * 2;
    }
    // Change code above this line
}

class Square : Shape
{
    float length;

    public Square(float length)
    {
        this.length = length * length;
        this.perimeter = calculatePerimeter();
    }

    // Change code below this line
    public float getArea()
    {
        return length * length;
    }

    protected float calculatePerimeter()
    {
        return 4 * length;
    }
    // Change code above this line
}

class Circle : Shape
{
    float radius;

    public Circle(float radius)
    {
        this.radius = radius;
        this.perimeter = calculatePerimeter();
    }

    // Change code below this line
    public float getArea()
    {
        return 3.14f * radius * radius;
    }

    protected float calculatePerimeter()
    {
        return 2.00f * 3.14f * radius;
    }
    // Change code above this line
}

class ConsoleApp
{
    static void Main()
    {
        List<Shape> shapes = new List<Shape>();
        shapes.Add(new Rectangle(10f, 20f));
        shapes.Add(new Square(10f));
        shapes.Add(new Circle(10f));

        foreach (Shape shape in shapes)
        {
            Console.WriteLine(shape.getArea());
        }
    }
}

Brug virtual-nøgleordet i basisklassen for at gøre metoderne overskrivelige.
Tilføj override-nøgleordet i metode-definitionerne i hver afledt klasse.

index.cs


              123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107
            
using System;
using System.Collections.Generic;

class Shape
{
    // Perimeter is the length of the 'outline' of a shape
    public float perimeter;

    // Change code below this line
    public virtual float getArea()
    {
        return 0.0f;
    }

    protected virtual float calculatePerimeter()
    {
        return 0.0f;
    }
    // Change code above this line
}

class Rectangle : Shape
{
    float width;
    float height;

    public Rectangle(float width, float height)
    {
        this.width = width;
        this.height = height;
        this.perimeter = this.calculatePerimeter();
    }

    // Change code below this line
    public override float getArea()
    {
        return width * height;
    }

    protected override float calculatePerimeter()
    {
        return width * 2 + height * 2;
    }
    // Change code above this line
}

class Square : Shape
{
    float length;

    public Square(float length)
    {
        this.length = length * length;
        this.perimeter = calculatePerimeter();
    }

    // Change code below this line
    public override float getArea()
    {
        return length * length;
    }

    protected override float calculatePerimeter()
    {
        return 4 * length;
    }
    // Change code above this line
}

class Circle : Shape
{
    float radius;

    public Circle(float radius)
    {
        this.radius = radius;
        this.perimeter = calculatePerimeter();
    }

    // Change code below this line
    public override float getArea()
    {
        return 3.14f * radius * radius;
    }

    protected override float calculatePerimeter()
    {
        return 2.00f * 3.14f * radius;
    }
    // Change code above this line
}

class ConsoleApp
{
    static void Main()
    {
        List<Shape> shapes = new List<Shape>();
        shapes.Add(new Rectangle(10f, 20f));
        shapes.Add(new Square(10f));
        shapes.Add(new Circle(10f));

        foreach (Shape shape in shapes)
        {
            Console.WriteLine(shape.getArea());
        }
    }
}

Var alt klart?

Tak for dine kommentarer!

Sektion 5. Kapitel 5