designing application using polymorphism

Question

I have created a polymorphic system, but I don't know whether this is the correct way of doing it. Am I abusing Polymorphism here? Here is the code:

class WriteObj
{
    public string Obj1 { get; set; }
    public string Obj2 { get; set; }
    public string Obj3 { get; set; }
}

The above code is a data object that I am passing around in the methods, since I would be using a List of these objects.

abstract class BaseWriter
{
    public abstract void Write(List<WriteObj> writeObjList);
}

class ConsoleWriter : BaseWriter
{
    public override void Write(List<WriteObj> writeObjList)
    {
        for (int i = 0; i < writeObjList.Count; i++)
        {
            Console.Writeline("I am in Console Writer, parameter: " + writeObjList[i].Obj1);
        }

    }
}

class FileWriter : BaseWriter
{
    public override void Write(List<WriteObj> writeObjList)
    {
        for (int i = 0; i < writeObjList.Count; i++)
        {
            Console.Writeline("I write in file, parameter: " + writeObjList[i].Obj1);
        }
    }
}

class DatabaseWriter : BaseWriter
{
    public override void Write(List<WriteObj> writeObjList)
    {
        for (int i = 0; i < writeObjList.Count; i++)
        {
            Console.Writeline("I write in database, parameter: " + writeObjList[i].Obj2);
        }
    }
}

In my main method I call them like:

    static void main()
    {
        List<WriteObj> col = new List<WriteObj>();
        col.AddRange(new WriteObj[2] { new WriteObj { Obj1 = "this is obj1 iteration 1", Obj2 = "This is obj2 iteration 1" }, 
            new WriteObj { Obj1 = "this is obj1 iteration 2", Obj2 = "This is obj2 iteration 2" } });

        //some factory will generate these concrete types, 
        //but the sake of simplicity I am instantiating it like that.
        BaseWriter a = new ConsoleWriter();
        a.Write(col);

        BaseWriter b = new FileWriter();
        b.Write(col);

        BaseWriter c = new DatabaseWriter();
        c.Write(col);
    }

Is it Ok to pass List of WriteObj in the Write method of the respective concrete implementations?

---

Update : I have used abstract class because it will be having some methods in it. I haven't mentioned it here for the sake of simplicity.

Answer 1

Yes, I don't see a problem with that.

If you don't have any implementation at all in the base class, consider making it an interface instead:

interface IWriter {
    void Write(List<WriteObj> writeObjList);
}

class ConsoleWriter : IWriter {
  public void Write(List<WriteObj> writeObjList) {
    foreach (WriteObj obj in writeObjList) {
      Console.Writeline("I am in Console Writer, parameter: " + obj.Obj1);
    }
  }
}

etc.

Answer 2

Yes, you could take that way. I would recomend to make BaseWriter an interface IWriter too. But I have an other suggestion.

interface IWriter
{
    void Write(List<WriteObject> writeObjectList);
}

public class ConsoleWriter : IWriter
{
    public void Write(List<WriteObject> writeObjectList)
    {
        // your implementation
    }
}

public class Writer // bad name but I dont have a better now
{
    private IWriter _writer; // or make it public and delete the constructor

    public Writer(IWriter writer)
    {
        _writer = writer;
    }

    public void Write(List<WriteObject> writeObjectList)
    {
        _writer.Write(writeObjectList);
    }
}

In this case, you do not use polymorphism. So your design is more flexible. You could change the way of writing your objects while runtime. Give it a try ;-)