Facade

Context: Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher‑level interface that makes the subsystem easier to use.

public class SubsystemA { public void A1() { } }
public class SubsystemB { public void B1() { } }
public class SubsystemC { public void C1() { } }

public class Facade
{
    private SubsystemA _a = new();
    private SubsystemB _b = new();
    private SubsystemC _c = new();
    public void Operation()
    {
        _a.A1();
        _b.B1();
        _c.C1();
    }
}

Real-world usage example

Order processing system: A OrderFacade calls inventory, payment, shipping, and notification subsystems in the correct order, hiding complexity from the client.

Example: In .NET, HttpClient provides a facade over lower‑level socket, DNS, and TLS components. Also, DbContext in EF Core is a facade over connection, command, transaction objects.

Related sections

• 5.2 Structural patterns
• 5.2.3 Decorator
• 5.2.5 Bridge