What is the function of the "this" keyword in a constructor?

Question

I was looking at sample code from MSDN just now and came accross:

namespace IListSourceCS
{
    public class Employee : BusinessObjectBase
    {
        private string      _id;
        private string      _name;
        private Decimal     parkingId;

        public Employee() : this(string.Empty, 0) {} // <<--- WHAT IS THIS???
        public Employee(string name) : this(name, 0) {}

score 16 · Accepted Answer · edited Jun 10 '11 at 18:29

16

It calls the other constructor in that class with that signature. Its a way of implementing the constructor in terms of other constructors. base can also be used to call the base class constructor. You have to have a constructor of the signature that matches this for it to work.

edited Jun 10 '11 at 18:29

Steve Guidi

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answered Apr 13 '11 at 02:15

Craig Suchanec

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MS code coverage test complaints about this. Do you know how to write a unit test for it. – Tun Jan 31 '14 at 15:39
2

@coder Sorry I have never used the MS code coverage and without greater detail about exactly what the problem is I can't really even begin to guess what the problem is – Craig Suchanec Feb 05 '14 at 16:33

Sanjeevakumar Hiremath · Answer 2 · 2011-04-13T02:41:42.883

8

this lets you call another constructor of Employee (current) class with (string, int) parameters.

This is a technique to initialize an object known as Constructor Chaining

edited Apr 13 '11 at 02:41

answered Apr 13 '11 at 02:15

Sanjeevakumar Hiremath

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score 3 · Answer 3 · edited Sep 21 '22 at 13:47

This sample might help some of the different derivations... The first obviously has two constructor methods when an instance is created... such as

FirstClass oTest1 = new FirstClass();

or

FirstClass oTest1b = new FirstClass(2345);

The SECOND class is derived from FirstClass. notice it too has multiple constructors, but one is of two parameters... The two-parameter signature makes a call to the "this()" constructor (of the second class)... Which in-turn calls the BASE CLASS (FirstClass) constructor with the integer parameter...

So, when creating classes derived from others, you can refer to its OWN class constructor method, OR its base class... Similarly in code if you OVERRIDE a method, you can do something IN ADDITION to the BASE() method...

Yes, more than you may have been interested in, but maybe this clarification can help others too...

   public class FirstClass
   {
      int SomeValue;

      public FirstClass()
      { }

      public FirstClass( int SomeDefaultValue )
      {
         SomeValue = SomeDefaultValue;
      }
   }


   public class SecondClass : FirstClass
   {
      int AnotherValue;
      string Test;

      public SecondClass() : base( 123 )
      {  Test = "testing"; }

      public SecondClass( int ParmValue1, int ParmValue2 ) : this()
      {
         AnotherValue = ParmValue2;
      }
   }

in your example, is it the case that if you took away the call to this(), the base class constructor would not execute? — Aaron Anodide, Apr 13 '11 at 02:42
@Gabriel, no, but if I had other constructors that I DID want to call OF the same class, I would just apply those parameters... much like the original post showed a forced call with empty string and zero value... — DRapp, Apr 13 '11 at 03:32

score -1 · Answer 4 · edited May 23 '17 at 12:32

A constructor is a special method/function that is ran to initialize the object created based on the class. This is where you run initialization things, as setting default values, initializes members in all ways.

"this" is a special word which points so the very own object you're in. See it as the objects refereence within the object itself used to access internal methods and members.

Check out the following links :

What is the function of the "this" keyword in a constructor?

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