Proxy pattern is commonly used in distributed algorithms.

What it looks like

Let’s start with this example provided by Wikipedia: Proxy pattern:

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 interface ICar
{
    void DriveCar();
}

// Real Object
public class Car : ICar
{
    public void DriveCar()
    {
        Console.WriteLine("Car has been driven!");
    }
}

// Proxy Object
public class ProxyCar : ICar
{
    private Driver driver;
    private ICar realCar;

    public ProxyCar(Driver driver)
    {
        this.driver = driver;
        this.realCar = new Car();
    }

    public void DriveCar()
    {
        if (driver.Age < 16)
            Console.WriteLine("Sorry, the driver is too young to drive.");
        else
            this.realCar.DriveCar();
     }
}

public class Driver
{
    public int Age { get; set; }

    public Driver(int age)
    {
        this.Age = age;
    }
}

// How to use above Proxy class?
private void btnProxy_Click(object sender, EventArgs e)
{
    ICar car = new ProxyCar(new Driver(15));
    car.DriveCar();

    car = new ProxyCar(new Driver(25));
    car.DriveCar();
}

Based on the code I could draw this UML:

When to use it

Use proxy when you want to add new functions/change how components communicate but do not want to change the existing component (the Real Subject).

  • A proxy is a wrapper or agent object that is being called by the client to access the real serving object behind the scenes.
  • For the client, usage of a proxy object is similar to using the real object, because both implement the same interface.