C# base Keyword
Description
The base keyword is similar to the this keyword. It serves two essential purposes:
Accessing an overridden function member from the subclass Calling a base class constructor
Syntax
'base' refers to the base class of the derived class in which it is used. This usage has the following general form:
base.member Example
The following code uses base keyword to access field in the base class.
using System;/*from w w w . ja v a 2 s. com*/
class BaseClass
{
public string Field1 = "In the base class";
}
class DerivedClass : BaseClass
{
new public string Field1 = "In the derived class";
public void Display()
{
Console.WriteLine("{0}", Field1); // Access the derived class.
Console.WriteLine("{0}", base.Field1); // Access the base class.
}
}
class Program
{
static void Main()
{
DerivedClass oc = new DerivedClass();
oc.Display();
}
}
The code above generates the following result.
Example 2
The following code shows how to call constructor from base class with base keyword.
using System;// w w w.ja va 2 s .c om
public class BaseClass
{
public BaseClass(int x)
{
this.x = x;
}
public int X
{
get
{
return(x);
}
}
int x;
}
public class Derived: BaseClass
{
public Derived(int x): base(x)
{
}
}
class MainClass
{
public static void Main()
{
Derived d = new Derived(15);
Console.WriteLine("X = {0}", d.X);
}
}
The code above generates the following result.
What is name hiding
An example of inheritance-related name hiding.
using System; //from w w w . ja v a 2s . c o m
class BaseClass {
public int i = 0;
}
// Create a derived class.
class DerivedClass : BaseClass {
new int i; // this i hides the i in BaseClass
public DerivedClass(int b) {
i = b; // i in DerivedClass
}
public void show() {
Console.WriteLine("i in derived class: " + i);
}
}
class MainClass {
public static void Main() {
DerivedClass ob = new DerivedClass(2);
ob.show();
}
}
The code above generates the following result.
Example 3
The following code shows to how to use base to overcome name hiding.
using System; /*from w w w. java 2 s . c om*/
class BaseClass {
public int i = 0;
}
// Create a derived class.
class DerivedClass : BaseClass {
new int i; // this i hides the i in BaseClass
public DerivedClass(int a, int b) {
base.i = a; // this uncovers the i in BaseClass
i = b; // i in DerivedClass
}
public void show() {
// this displays the i in BaseClass.
Console.WriteLine("i in base class: " + base.i);
// this displays the i in DerivedClass
Console.WriteLine("i in derived class: " + i);
}
}
class MainClass {
public static void Main() {
DerivedClass ob = new DerivedClass(1, 2);
ob.show();
}
}
The code above generates the following result.
Example 4
How to call a hiddel method from parent class
using System; // w ww . ja v a2 s . c o m
class BaseClass {
public int i = 0;
// show() in BaseClass
public void show() {
Console.WriteLine("i in base class: " + i);
}
}
// Create a derived class.
class DerivedClass : BaseClass {
new int i; // this i hides the i in BaseClass
public DerivedClass(int a, int b) {
base.i = a; // this uncovers the i in BaseClass
i = b; // i in DerivedClass
}
// This hides show() in BaseClass. Notice the use of new.
new public void show() {
base.show(); // this calls show() in BaseClass
// this displays the i in DerivedClass
Console.WriteLine("i in derived class: " + i);
}
}
class MainClass {
public static void Main() {
DerivedClass ob = new DerivedClass(1, 2);
ob.show();
}
}
The code above generates the following result.
