C# Constructors and Inheritance

Description

A subclass must declare its own constructors.

Subclass must redefine any constructors it wants to expose.

It can call any of the base class's constructors with the base keyword.

For example,

/*from w w w . ja v a 2s .  c  o  m*/
public class Baseclass
{
  public int X;
  public Baseclass () { }
  public Baseclass (int x) { this.X = x; }
}

public class Subclass : Baseclass
{
  public Subclass (int x) : base (x) { }
}

Note

The base keyword works rather like the this keyword, except that it calls a constructor in the base class.

Base class constructors always execute first; this ensures that base initialization occurs before specialized initialization.

For Implicit calling of the parameterless base class constructor. If a constructor in a subclass omits the base keyword, the base type's parameter-less constructor is implicitly called:

public class BaseClass
{/*from  w  w w  .  j  a  v  a 2s.  c om*/
  public int X;
  public BaseClass() { X = 1; }
}

public class Subclass : BaseClass
{
  public Subclass() { Console.WriteLine (X); }  // 1
}

If the base class has no parameterless constructor, subclasses are forced to use the base keyword in their constructors.