Question

I would like to understand what Implement Interface Explicitly entails in C# based on the contexts/scenarios described below. Lets say I have the following interface:

public interface ITestService
{
    void Operation1();
    void Operation2();
}

Lets say I implement the interface explicitly as shown below, is it possible, using whatever means to call Operation2() from Operation1()?

public sealed class TestService : ITestService
{
    public TestService(){}

    void ITestService.Operation1()
    {
        // HOW WOULD ONE SUCCESSFULLY INVOKE Operation2() FROM HERE. Like:
        Operation2();
    }

    void ITestService.Operation2()
    {

    }
}

What happens differently (under the wraps) to allow testService1 and testService2 declared differently below behave differently?

static class Program
{
    static void Main(string[] args)
    {
        ITestService testService1 = new TestService();      
        testService1.Operation1(); // => Works: WHY IS THIS POSSIBLE, ESPECIALLY SINCE Operation1() AND Operation2() WOULD BE *DEEMED* private?
        // *DEEMED* since access modifiers on functions are not permitted in an interface

        // while ...
        TestService testService2 = new TestService();
        testService2.Operation1(); //! Fails: As expected
    }
}

Answer 1

void ITestService.Operation1()
{
    ((ITestService)this).Operation2();
}

As for your second question:

All members of interfaces are public. Hence the implementation will be public too.