Constructor Initializers

Constructor Initializers

By default, the parameterless constructor of the base class is called when an object is being constructed. But constructors can be overloaded, so a base class might have more than one. If you want your derived class to use a specific base class constructor other than the parameterless constructor, you must specify it in a constructor initializer.

There are two forms of constructor initializers:

• The first form uses the keyword base and specifies which base class constructor to use.
• The second form uses the keyword this and specifies which other constructor from this class should be used.

Using base Keyword Form

Use following syntax:

public [Derived Class]([parameter list]) : base([parameter list])
{
 ....
}

Look at following example:

class person
{
 public string firstName;
 public string lastName;
 public ushort age;
 public person(string FirstName,string LastName, ushort Age)
 {
  firstName = FirstName;
  lastName = LastName;
  age = Age;
 }
 .....
}

class employee : person
{
 public string company;

 public employee(string FirstName, string LastName, ushort Age, string Company):base(FirstName,LastName,Age)
 {
  company = Company;
 }
 ....
}

class Program
{
 static void Main(string[] args)
 {
  employee me=new employee("Yang", "Sopiana", 29, "Company.inc");
  ....
 }
}

Using this Keyword Form

The other form of constructor initializer instructs the construction process (actually, the compiler) to use a different constructor from the same class. For example, the following shows a constructor with a single parameter for class MyClass. That single-parameter constructor, however, uses a constructor from the same class, but with two parameters, supplying a default parameter as the second one. See following syntax:

public [Class Name]([parameter list]): this([parameter list])
{ 
 ....
}

Following code snipet show you how to use the syntax:

class person
{
 public string firstName;
 public string lastName;
 public ushort age;
 public person(string FirstName)
 {
  firstName = FirstName;
 }

 public person(string FirstName, string LastName) : this(FirstName)
 {
  lastName = LastName;
 }

 public person(string FirstName, string LastName, ushort Age) : this(FirstName, LastName)
 {
  age = Age;
 }
 ....
}

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