Kody źródłowe/Pusty Obiekt (wzorzec projektowy)

Java

/** AbstractObject */
public interface Shape2D {

    void move(double x, double y);
}

/** RealObject */
public class Circle implements Shape2D {

    @Override
    public void move(double x, double y) {
        System.out.println("Shape has been moved by vector(" + x + "," + y + ")");
    }
}

/** NullObject */
public class NullShape2D implements Shape2D {

    @Override
    public void move(double x, double y) {
        // do nothing
    }
}

/** Client program */
public class NullObjectExample {

    public static void main(String[] args) { 

        Shape2D[] shapes = { new NullShape2D(), new Circle(), new NullShape2D(), new Circle() };

        /* zamiast za każdym razem sprawdzać warunek, czy referencja posiada wartość pustą
         *for (int i = 0; i < shapes.length; i++) {
         *   if (shapes[i] != null) {
         *      shapes[i].move(i, i);
         *   }
         *}
         * Stosuje się wzorzec Pusty Obiekt
         */
        for (int i = 0; i < shapes.length; i++) {
            shapes[i].move(i, i);
        }
    }
}

C#

using System;
 
/** AbstractObject */
interface IAnimal
{
    void MakeSound();
}
 
/** RealObject */
class Dog : IAnimal
{
    public void MakeSound()
    {
        Console.WriteLine("Woof!");
    }
}
 
/** NullObject */
class NullAnimal : IAnimal
{
    public void MakeSound()
    {
        // Purposefully provides no behaviour.
    }
}
 
/** Client program */
static class Program
{
    static void Main()
    {
        IAnimal dog = new Dog();
        dog.MakeSound(); // outputs "Woof!"
 
        /* Instead of using C# null, use a NullAnimal instance.
         * This example is simplistic but conveys the idea that if a NullAnimal instance is used then the program
         * will never experience a .NET System.NullReferenceException at runtime, unlike if C# null was used.
         */
        IAnimal unknown = new NullAnimal();  //<< replaces: IAnimal unknown = null;
        unknown.MakeSound(); // outputs nothing, but does not throw a runtime exception        
    }
}