C# 0 The Complete Reference

PART I

C h a p t e r   1 1 :  

I n h e r i t a n c e  

283

PART IPART I

Here is an example of name hiding:

// An example of inheritance-related name hiding.

using System;

class A {

  public int i = 0;

}

// Create a derived class.

class B : A {

  new int i; // this i hides the i in A

  public B(int b) {

    i = b; // i in B

  }

  public void Show() {

    Console.WriteLine("i in derived class: " + i);

  }

}

class NameHiding {

  static void Main() {

    B ob = new B(2);

    ob.Show();

  }

}

First, notice the use of 

new

 in this line.

new int i; // this i hides the i in A

In essence, it tells the compiler that you know a new variable called 

i

 is being created that 

hides the 

i

 in the base class 

A

. If you leave 

new

 out, a warning is generated.

The output produced by this program is shown here:

i in derived class: 2

Since

B

 defines its own instance variable called 

i

, it hides the 

i

 in 

A

. Therefore, when 

Show( )

is invoked on an object of type 

B

, the value of 

i

 as defined by 

B

 is displayed—not the one 

defined in 

A

.

Using base to Access a Hidden Name

There is a second form of 

base

 that acts somewhat like 

this

, except that it always refers to the 

base class of the derived class in which it is used. This usage has the following general form:

base.

member

Here, 

member

 can be either a method or an instance variable. This form of 

base

 is most 

applicable to situations in which member names of a derived class hide members by the 

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284

 

P a r t   I :  

T h e   C #   L a n g u a g e

same name in the base class. Consider this version of the class hierarchy from the preceding 

example:

// Using base to overcome name hiding.

using System;

class A {

  public int i = 0;

}

// Create a derived class.

class B : A {

  new int i; // this i hides the i in A

  public B(int a, int b) {

    base.i = a; // this uncovers the i in A

    i = b; // i in B

  }

  public void Show() {

    // This displays the i in A.

    Console.WriteLine("i in base class: " + base.i);

    // This displays the i in B.

    Console.WriteLine("i in derived class: " + i);

  }

}

class UncoverName {

  static void Main() {

    B ob = new B(1, 2);

    ob.Show();

  }

}

This program displays the following:

i in base class: 1

i in derived class: 2

Although the instance variable 

i

 in 

B

 hides the 

i

 in 

A

,

base

 allows access to the 

i

 defined in 

the base class.

Hidden methods can also be called through the use of 

base

. For example, in the 

following code, class 

B

 inherits class 

A

, and both 

A

 and 

B

 declare a method called 

Show( )

.

Inside,

B

’s

Show( )

, the version of 

Show( )

 defined by 

A

 is called through the use of 

base

.

// Call a hidden method.

using System;

class A {

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