How to avoid duplication?

Question

I'm making a C# application. The application has two classes and multiple methods. While writing the code I stumbled on a problem. I use the same two variables (XList and YList) and one method in both classes. And probably I will need more classes with this code. So I created a duplication problem. Below is a simple version of my code:

public class A {
  private testEntities db = new testEntities();
  public List<int> XList = new List<int>();
  public List<int> YList = new List<int>();

  public void GetAllInfo()
  {
    // Get the data from a database and add to a list
    XList = db.Table1.ToList();
    YList = db.Table2.ToList();
  }

  public void DoStuff()
  {
    // Do Stuff with XList and YList
  }
}

public class B {
  private testEntities db = new testEntities();
  public List<int> XList = new List<int>();
  public List<int> YList = new List<int>();

  public void GetAllInfo()
  {
    // Get the data from a database and add to a list (the same as in class A)
    XList = db.Table1.ToList();
    YList = db.Table2.ToList();
  }

  public void DoDifferentStuff()
  {
    // Do ddifferent stuff with XList and YList then in class A
  }
}

My question is what is the best way to solve this duplication problem?

After some research I found that I can probably solve this with inheritance or composition. I also read that people choose composition over inheritance. So I wrote the following code to solve the duplication:

public class DataPreparation
{
  private testEntities db = new testEntities();
  public List<int> XList = new List<int>();
  public List<int> YList = new List<int>();

  public void GetAllInfo()
  {
    // Get the data from a database and add to a list
    XList = db.Table1.ToList();
    YList = db.Table2.ToList();
  }

  // Implement other methods
}

public class A 
{
  public void MethodName()
  { 
    DataPreparation dataPreparation = new DataPreparation();
    dataPreparation.GetAllInfo();

    UseDataX(dataPreparation.XList);
    UseDataY(dataPreparation.YList);

    // Implementation UseDataX() and UseDataY()
  }
}

public class B 
{
  public void MethodName()
  { 
    DataPreparation dataPreparation = new DataPreparation();
    dataPreparation.GetAllInfo();

    VisualizeDataX(dataPreparation.XList);
    VisualizeDataY(dataPreparation.YList);

    // Implementation VisualizeDataX() and VisualizeDataY()
  }
}

As you can see I made a class that handles getting the data from the database. And that the class A and B use the DataPreparation class. But is this the best way to solve the duplication? Or should I use inheritance or something different?

Answer 1

I think you should probably only have one method called DoStuff() rather than one called DoStuff() and another called DoDifferentStuff() .

Then you can create an ABC to implement the common code, and have an abstract DoStuff() method that is implemented differently in the derived classes:

public abstract class Base
{
    private testEntities db = new testEntities();

    public List<int> XList = new List<int>();
    public List<int> YList = new List<int>();

    public void GetAllInfo()
    {
        // Get the data from a database and add to a list (the same as in class A)
        XList = db.Table1.ToList();
        YList = db.Table2.ToList();
    }

    public abstract void DoStuff();
}

public class A: Base
{
    public override void DoStuff()
    {
        // Do Stuff with XList and YList
    }
}

public class B: Base
{
    public override void DoStuff()
    {
        // Do ddifferent stuff with XList and YList then in class A
    }
}

(I also think it's a bad idea to have public fields like that - but I'm guessing/hoping that this is just sample code and your real code doesn't have those...)

Other code (except code that creates an A or a B ) would use the object via the Base class type.

Answer 2

One simple option is to use inheritance . Make a base class with the shared functionality and the A and B can inherit from that. For example:

public abstract class Base
{
    private testEntities db = new testEntities();
    public List<int> XList = new List<int>();
    public List<int> YList = new List<int>();

    public void GetAllInfo()
    {
        // Get the data from a database and add to a list
        XList = db.Table1.ToList();
        YList = db.Table2.ToList();
    }
}

public class A : Base
{
    public void DoStuff()
    {
        // Do Stuff with XList and YList
    }
}

public class B : Base
{
    public void DoDifferentStuff()
    {
        // Do ddifferent stuff with XList and YList then in class A
    }
}