CHAPTER 7 CLASSES AND INHERITANCE

Hiding Members of a Base Class

Although a derived class cannot delete any of the members it has inherited, it can hide them.

•To hide an inherited data member, declare a new member of the same type and with the same name.

•You can hide, or mask, an inherited function member by declaring in the derived class a new function member with the same signature. Remember that the signature consists of the name and parameter list but does not include the return type.

•To let the compiler know that you are purposely hiding an inherited member, use the new modifier. Without it, the program will compile successfully, but the compiler will warn you that you are hiding an inherited member.

•You can also hide static members.

The following code declares a base class and a derived class, each with a string member called Field1. The keyword new is used to explicitly tell the compiler to mask the base class member. Figure 7-4 illustrates an instance of each class.

Figure 7-4. Hiding a member of a base class

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CHAPTER 7 CLASSES AND INHERITANCE

In the following code, OtherClass derives from SomeClass but hides both its inherited members. Note the use of the new modifier. The code is illustrated in Figure 7-5.

↑{ Console.WriteLine("OtherClass.Method1: {0}", value); }

}Keyword

Figure 7-5. Hiding a field and a method of the base class

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CHAPTER 7 CLASSES AND INHERITANCE

Base Access

If your derived class absolutely must access a hidden inherited member, you can access it by using a base access expression. This expression consists of the keyword base, followed immediately by a period and the name of the member, as shown here:

Console.WriteLine("{0}", base.Field1);

↑

Base access

For example, in the following code, derived class OtherClass hides Field1 in its base class but accesses it by using a base access expression.

class Program { static void Main()

{

OtherClass oc = new OtherClass(); oc.PrintField1();

}

}

This code produces the following output:

Field1 -- In the derived class

Field1 -- In the base class

If you use this feature frequently, you might want to revaluate the design of your classes. Generally there are more elegant designs, but the feature is there if there’s a situation where nothing else will do.

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