Inheritance

A class can inherit from another class to extend or customize the original class. Inheriting from a class lets you reuse the functionality in that class instead of building it from scratch. A class can inherit from only a single class, but can itself be inherited by many classes, thus forming a class hierarchy. In this example, we start by defining a class called Asset:

public class Asset { public string Name; }

Next, we define classes called Stock and House, which will inherit from Asset. Stock and House get everything an Asset has, plus any additional members that they define:

public class Stock : Asset   // inherits from Asset
{
  public long SharesOwned;
}

public class House : Asset   // inherits from Asset
{
  public decimal Mortgage;
}

Here’s how we can use these classes:

Stock msft = new Stock { Name="MSFT",
                         SharesOwned=1000 };

Console.WriteLine (msft.Name);         // MSFT
Console.WriteLine (msft.SharesOwned);  // 1000

House mansion = new House { Name="Mansion",
                            Mortgage=250000 };

Console.WriteLine (mansion.Name);      // Mansion
Console.WriteLine (mansion.Mortgage);  // 250000

The subclasses, Stock and House, inherit the Name property from the base class, Asset.

Subclasses are also called derived classes.

Polymorphism

References are polymorphic. This means a variable of type x can refer to an object that subclasses x. For instance, consider the following method:

public static void Display (Asset asset)
{
  System.Console.WriteLine (asset.Name);
}

This method can display both a Stock and a House ...

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