Should i definitely have a constructor in a derived class?

Question

My problem is like this. I have a XMLUtility class

public class XmlUtility
    {

        protected string FilePath;

        protected string XMLFileName;

        protected XmlDocument SettingsFile;


        public XmlUtility(string inFilePath, string inXMLFileName)
        {    

            FilePath = inFilePath;
            XMLFileName = inXMLFileName;    

            if (isFilePresent() == false)
            {                    
                createXMLFile();                   
            }

            else
            {
                SettingsFile = new XmlDocument();
                SettingsFile.Load(FilePath + "\\" + XMLFileName);    
            }   

        }

and a

public bool isFilePresent()
        {                
            return File.Exists(FilePath + "\\" + XMLFileName) ? true : false;

        }

and other basic functions such as addSetting, removeSetting, checkSettingExists etc. This class provides functionality for very basic xml settings file.

So now i need a bit more advanced handling of settings. So i created another class and derived it from the XMLUtility class.

public class KeyPairingXML : XmlUtility
    {




    }

So my initial thought was i don't need to have a constructor for this class as it will call the base classes constructor. But i was wrong.

 public KeyPairingXML(string inFilePath, string inXMLFileName) : base(inFilePath, inXMLFileName)
        {



        }

My question is whether the code above correct? Do i need to write the whole checking process inside this constructor as well or will that be handled by the base class's constructor? Just an empty code block is correct?

Answer 1

Not sure which language you are using, but for most (such as Java or C#) you can ommit defining a constructor in a derived type if:

1. The base class does not define a constructor (therefore it has an implicit default constructor)
2. The base class defines a no-argument constructor. In this case it can have other constructors and it won't change things

However, your base class only defined a non-default constructor so you need to redefine it in the derived class. The following code you have is correct:

public KeyPairingXML(string inFilePath, string inXMLFileName)
  : base(inFilePath, inXMLFileName) {
}

You should also be able to call the public method on the base class. Are you seeing any errors/warnings?