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Impara Sfida: Polimorfismo | Principi OOP
C# Oltre le Basi

bookSfida: Polimorfismo

Il programma riportato di seguito contiene una superclasse chiamata Shape e tre classi derivate chiamate Rectangle, Square e Circle. Il problema del codice è che i metodi non sono correttamente sovrascritti, poiché l'output mostra 0.0 per tutte e tre le istruzioni Console.WriteLine, il che implica che vengono eseguiti i metodi della classe base invece di quelli delle classi derivate.

Modifica il codice in modo che i due metodi, ovvero getArea e calculatePerimeter, siano correttamente sovrascritti.

index.cs

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()); } } }
  1. Nella classe base, utilizzare la parola chiave virtual per rendere i metodi sovrascrivibili.
  2. In ogni classe derivata, aggiungere la parola chiave override nelle definizioni dei metodi.
index.cs

index.cs

copy
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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 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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Sezione 5. Capitolo 5

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bookSfida: Polimorfismo

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Il programma riportato di seguito contiene una superclasse chiamata Shape e tre classi derivate chiamate Rectangle, Square e Circle. Il problema del codice è che i metodi non sono correttamente sovrascritti, poiché l'output mostra 0.0 per tutte e tre le istruzioni Console.WriteLine, il che implica che vengono eseguiti i metodi della classe base invece di quelli delle classi derivate.

Modifica il codice in modo che i due metodi, ovvero getArea e calculatePerimeter, siano correttamente sovrascritti.

index.cs

index.cs

copy
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()); } } }
  1. Nella classe base, utilizzare la parola chiave virtual per rendere i metodi sovrascrivibili.
  2. In ogni classe derivata, aggiungere la parola chiave override nelle definizioni dei metodi.
index.cs

index.cs

copy
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()); } } }
Tutto è chiaro?

Come possiamo migliorarlo?

Grazie per i tuoi commenti!

Sezione 5. Capitolo 5
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