Remoting and Interfaces interview questions

What is .NET Remoting?
.NET Remoting allows objects to interact with one another across application domains.


What are the 2 message encoding formats supported by .NET Remoting and when do you choose one over the other?
Message Encoding Formats:
1. Binary encoding.
2. XML encoding.


Applications can use binary encoding where performance is critical, or XML encoding where interoperability with other remoting frameworks is essential.


What are the two types of .NET remote objects?
1. Client-activated objects - Client-activated objects are under the control of a lease-based lifetime manager that ensures that the object is garbage collected when its lease expires.
2. Server-activated objects - In the case of server-activated objects, developers have a choice of selecting either a "single call" or "singleton" model. The lifetime of singletons are also controlled by lease-based lifetime.


What is considered as Remote Object?
Any object outside the application domain of the calling appication is considered remote object, even if the objects are executing on the same machine.

 Can you treat every object as a remote object?
Objects that cannot be serialized cannot be passed to a different application domain and are therefore nonremotable.


What are the ways in which an object can be serialized?
1. Mark your class with serializable attribute.
2. Make your class implement ISerializable interface.


How can you change an object into a remote object?
Any object can be changed into a remote object by deriving it from MarshalByRefObject.


What happens when a client activates a remote object?
When a client activates a remote object, it receives a proxy to the remote object. All operations on this proxy are appropriately indirected to enable the remoting infrastructure to intercept and forward the calls appropriately.


What are proxy objects and what is the use of these proxy objects?
Proxy objects are created when a client activates a remote object. The proxy object acts as a representative of the remote object and ensures that all calls made on the proxy are forwarded to the correct remote object instance.

Explain what is an Interface in C#?
An Interface in C# is created using the interface keyword. An example is shown below.

using System;
namespace Interfaces
{
interface IBankCustomer
{
void DepositMoney();
void WithdrawMoney();
}
public class Demo : IBankCustomer
{
public void DepositMoney()
{
Console.WriteLine("Deposit Money");
}

public void WithdrawMoney()
{
Console.WriteLine("Withdraw Money");
}

public static void Main()
{
Demo DemoObject = new Demo();
DemoObject.DepositMoney();
DemoObject.WithdrawMoney();
}
}
}

In our example we created IBankCustomer interface. The interface declares 2 methods.
1. void DepositMoney();
2. void WithdrawMoney();

Notice that method declarations does not have access modifiers like public, private, etc. By default all interface members are public. It is a compile time error to use access modifiers on interface member declarations. Also notice that the interface methods have only declarations and not implementation. It is a compile time error to provide implementation for any interface member. In our example as the Demo class is inherited from the IBankCustomer interface, the Demo class has to provide the implementation for both the methods (WithdrawMoney() and DepositMoney()) that is inherited from the interface. If the class fails to provide implementation for any of the inherited interface member, a compile time error will be generated. Interfaces can consist of methods, properties, events, indexers, or any combination of those four member types. When a class or a struct inherits an interface, the class or struct must provide implementation for all of the members declared in the interface. The interface itself provides no functionality that a class or struct can inherit in the way that base class functionality can be inherited. However, if a base class implements an interface, the derived class inherits that implementation.

Can an Interface contain fields?
No, an Interface cannot contain fields.


What is the difference between class inheritance and interface inheritance?
Classes and structs can inherit from interfaces just like how classes can inherit a base class or struct. However there are 2 differences.
1. A class or a struct can inherit from more than one interface at the same time where as A class or a struct cannot inherit from more than one class at the same time. An example depicting the same is shown below.

using System;
namespace Interfaces
{
interface Interface1
{
void Interface1Method();
}
interface Interface2
{
void Interface2Method();
}
class BaseClass1
{
public void BaseClass1Method()
{
Console.WriteLine("BaseClass1 Method");
}
}
class BaseClass2
{
public void BaseClass2Method()
{
Console.WriteLine("BaseClass2 Method");
}
}

//Error : A class cannot inherit from more than one class at the same time
//class DerivedClass : BaseClass1, BaseClass2
//{
//}

//A class can inherit from more than one interface at the same time
public class Demo : Interface1, Interface2
{
public void Interface1Method()
{
Console.WriteLine("Interface1 Method");
}

public void Interface2Method()
{
Console.WriteLine("Interface2 Method");
}

public static void Main()
{
Demo DemoObject = new Demo();
DemoObject.Interface1Method();
DemoObject.Interface2Method();
}
}
}

2. When a class or struct inherits an interface, it inherits only the method names and signatures, because the interface itself contains no implementations.

Can an interface inherit from another interface?
Yes, an interface can inherit from another interface. It is possible for a class to inherit an interface multiple times, through base classes or interfaces it inherits. In this case, the class can only implement the interface one time, if it is declared as part of the new class. If the inherited interface is not declared as part of the new class, its implementation is provided by the base class that declared it. It is possible for a base class to implement interface members using virtual members; in that case, the class inheriting the interface can change the interface behavior by overriding the virtual members.

Can you create an instance of an interface?
No, you cannot create an instance of an interface.

If a class inherits an interface, what are the 2 options available for that class?
Option 1: Provide Implementation for all the members inheirted from the interface.

namespace Interfaces
{
interface Interface1
{
void Interface1Method();
}

class BaseClass1 : Interface1
{
public void Interface1Method()
{
Console.WriteLine("Interface1 Method");
}
public void BaseClass1Method()
{
Console.WriteLine("BaseClass1 Method");
}
}
}

Option 2: If the class does not wish to provide Implementation for all the members inheirted from the interface, then the class has to be marked as abstract.

namespace Interfaces
{
interface Interface1
{
void Interface1Method();
}

abstract class BaseClass1 : Interface1
{
abstract public void Interface1Method();
public void BaseClass1Method()
{
Console.WriteLine("BaseClass1 Method");
}
}
}

A class inherits from 2 interfaces and both the interfaces have the same method name as shown below. How should the class implement the drive method for both Car and Bus interface?
namespace Interfaces
{
interface Car
{
void Drive();
}
interface Bus
{
void Drive();
}

class Demo : Car,Bus
{
//How to implement the Drive() Method inherited from Bus and Car
}
}

To implement the Drive() method use the fully qualified name as shown in the example below. To call the respective interface drive method type cast the demo object to the respective interface and then call the drive method.

using System;
namespace Interfaces
{
interface Car
{
void Drive();
}
interface Bus
{
void Drive();
}

class Demo : Car,Bus
{
void Car.Drive()
{
Console.WriteLine("Drive Car");
}
void Bus.Drive()
{
Console.WriteLine("Drive Bus");
}

static void Main()
{
Demo DemoObject = new Demo();
((Car)DemoObject).Drive();
((Bus)DemoObject).Drive();
}
}
}

What do you mean by "Explicitly Implemeting an Interface". Give an example?
If a class is implementing the inherited interface member by prefixing the name of the interface, then the class is "Explicitly Implemeting an Interface member". The disadvantage of Explicitly Implemeting an Interface member is that, the class object has to be type casted to the interface type to invoke the interface member. An example is shown below.

using System;
namespace Interfaces
{
interface Car
{
void Drive();
}

class Demo : Car
{
// Explicit implementation of an interface member
void Car.Drive()
{
Console.WriteLine("Drive Car");
}

static void Main()
{
Demo DemoObject = new Demo();

//DemoObject.Drive();
// Error: Cannot call explicitly implemented interface method
// using the class object.
// Type cast the demo object to interface type Car
((Car)DemoObject).Drive();
}
}
}