Abstract Vs Interface

In this passage you will reach difference between abstract and interface.

Introduction;

In this article along with the demo project I will discuss Interfaces versus Abstract classes. The concept of Abstract classes and Interfaces is a bit confusing for beginners of Object Oriented programming. Therefore, I am trying to discuss the theoretical aspects of both the concepts and compare their usage. And finally I will demonstrate how to use them with C#.

Background;

An Abstract class without any implementation just looks like an Interface; however there are lot of differences than similarities between an Abstract class and an Interface. Let's explain both concepts and compare their similarities and differences.

What is an Interface?

An interface is not a class. It is an entity that is defined by the word Interface. An interface has no implementation; it only has the signature or in other words, just the definition of the methods without the body. As one of the similarities to Abstract class, it is a contract that is used to define hierarchies for all subclasses or it defines specific set of methods and their arguments. The main difference between them is that a class can implement more than one interface but can only inherit from one abstract class. Since C# doesn’t support multiple inheritance, interfaces are used to implement multiple inheritance.

Differences	Interface	Abstract
1	A class may have inherit several interfaces.	A class may inherit only one abstract class.
2	An interface cannot provide any code,just the signature.(After C#8.0 u can use interface like an abstract).	An abstract class can prodive complete,default code and/or just details that have to be overriden.
3	An interface cannot have access modifiers for the subs,functions,properties etc everything is assumed as public.	An abstract class can contain access modifiers for the subs,functions,properties.
4	Interfaces are used to define the peripheral abilities of a class.In other words both Human and Vehicle can inherit from a IMovable interface.	An abstract class defines the core identity of a class and there it is used for objects of the same type.
5	If various implementations only share method signatures then it is better to use Interfaces.	If various implementations are of the same kind and use common behaviour or status then abstract class is better to use.
6	In terms of speed; requires more time to find the actual method in the corresponding classes.	Fast
7	If we add a new method to an Interface then we have to track down all the implementattions of the interface and define implementation for the new method.	If we add a new method to an abstract class then we have the option of providing default implementation and therefore all the existing code might work properly.

Now let's see this difference at the code behind; Firstly we create Abstract class;

public abstract class Worker;

public string id;
public string FirstName;
public string LastName;
//properties

public abstract string ID
{
    get;
    set;
}
public abstract string FirstName
{
    get;
    set;
}

//completed methods

public String Add()
{ 
    return "Worker"+id+""+LastName+""+Firstname+"added";
}      

public String Delete()
{ 
    return "Worker"+id+""+LastName+""+Firstname+"deleted";
}      

public String Update()
{ 
    return "Worker"+id+""+LastName+""+Firstname+"updated";
}              

Now we create Interface class;

public interface IWorker
{
//In this fields , just signature of the properties and methods.
setting a rule or contract to be followed by implementations.

String Id
{
  get;
  set;
}

String Firstname
{
  get;
  set;
}

String LastName
{
  get;
  set;
}

//Can not have implementation cannot have modifiers public
all are assumed public.Cannot have virtual

String Update();
String Add();
String Delete();


  

Now get an object and inherit from both of them;

Firstly Abstract;

public class WorkerZone : Worker

//uses all the properties of the abstract class 
therefore no properties or fields here!

Public WorkerZone ()
{
}

public ovverride String ID
{
    get
    {
    return id;
    }
    set
    {
    id=value;
    }
}

public override String FirstName
{
    get
    {
    return FirstName;
    }
    set
    {
    FirstName=value
    }
}
///These methods that are implemented in the abstract class

public new String Add()
{
    return base.Add();
}
public new String Update()
{
    return base.Update();
}
public new String Delete();
{
    return base.Delete();
}
}

then now by using interface;

public class IWorkerZone : IWorker// "I" is commonly used for interface.
{

//****All the properties and fields defined here!!!***
    public String id;
    public String FirstName;
    public String LastName;
    
    public IWorkerZone()
    {
    
    //TODO:Add constructor logic here
    
    }
    
    public string id
    {
        get
        {
        return id;
        }
        set
        {
        id=value;
        }
    }
    
    public string FirstName
    {
        get 
        {
        return Firstname;
        }
        set
        { 
        Firstname=value;
        }
    }
    
    public string LastName
    {
        get
        {
        return LastName;
        }
        set
        {
        LastName=value;
        }
    }
    
    
        //all the manipulations including Add,Delete, 


        //Search, Update, Calculate are done

        //within the object as there are not 

        //implementation in the Interface entity.
        
        public String Add()
        {
            return "Fulltime Worker" + FirstName + " Added.";
        }
        
        public String Delete()
        {
            return "Fulltime Worker" + FirstName + " Deleted.";
        }
    
        public String Update()
        {
            return "Fulltime Worker" + FirstName + " Updated.";
        }

As a conclusion , interface doesn't let to change any properties on the subclasses.Because interface inherit the subclass static rule but in abstract you can override. Reference :CodeProject/ Rahman Mahmoodi guru99/Anonymous Stackoverflow/