Structural Pattern - Facade

Definition:

Provide a unified interface to a set of interfaces in a subsystem. Façade defines a higher-level interface that makes the subsystem easier to use. 

UML Diagram:  

Sample Code:

public sealed class Facade
    {
        SubSystem1 _subSystem1 = default(SubSystem1);
        SubSystem2 _subSystem2 = default(SubSystem2);
        SubSystem3 _subSystem3 = default(SubSystem3);

        public Facade()
        {
            _subSystem1 = new SubSystem1();
            _subSystem2 = new SubSystem2();
            _subSystem3 = new SubSystem3();
        }

        public void Method1()
        {
            _subSystem3.Method1();
            _subSystem1.Action1();
            _subSystem2.Action1();
        }

        public void Method2()
        {
            _subSystem1.Action2();
            _subSystem2.Action1();
            _subSystem2.Action2();
        }
    }

    public class SubSystem1
    {
        public void Action1()
        {
            Console.WriteLine("SubSystem1 -> Action1 called");
        }

        public void Action2()
        {
            Console.WriteLine("SubSystem1 -> Action2 called");
        }
    }
    public class SubSystem2
    {
        public void Action1()
        {
            Console.WriteLine("SubSystem2 -> Action1 called");
        }

        public void Action2()
        {
            Console.WriteLine("SubSystem2 -> Action2 called");
        }
    }

    public class SubSystem3
    {
        public void Method1()
        {
            Console.WriteLine("SubSystem3 -> Action1 called");
        }
    }