Constructors enable the programmer to set default
values, limit instantiation.
A special method of the class that will be
automatically invoked when an instance of the class is created is called as
constructor.
If you do not provide a constructor for your
object, C# will create one by default that instantiates the object and sets
member variables to the default values
Constructors are mainly used to initialize private fields of the class while creating an instance for the class.
When you are not creating a constructor in the class, then compiler will automatically create a default constructor in the class that initializes all numeric fields in the class to zero and all string and object fields to null.
Constructors are mainly used to initialize private fields of the class while creating an instance for the class.
When you are not creating a constructor in the class, then compiler will automatically create a default constructor in the class that initializes all numeric fields in the class to zero and all string and object fields to null.
Types of constructors:
Default Constructor
A constructor that takes no parameters is called
a default constructor. Default constructors are invoked whenever an object
is instantiated by using the new operator and no arguments are
provided to new.
If
a class does not have a constructor, a default constructor is automatically
generated and default values are used to initialize the object fields.
For
example, an int is
initialized to 0. For more information on default values
Private Constructors:
A private constructor is a special instance constructor.
It is generally used in classes that contain static members only.
If a class
has one or more private constructors and no public constructors, other classes
(except nested classes) cannot create instances of this class.
For example:
The declaration of the empty constructor prevents
the automatic generation of a default constructor. Note that if you do not use
an access modifier with the constructor it will still be private by default.
However, the private modifier
is usually used explicitly to make it clear that the class cannot be
instantiated.
When class contains a private constructor then we cannot create
a instance of that class.
Instance Constructors:
Instance constructors are used to create and
initialize any instance member variables when you use the new expression
to create an object of a class.
To
initialize a static class,
or static variables in a non-static class, you must define a static constructor
class CoOrds
{
public int x, y;
// constructor
public CoOrds()
{
x = 0;
y = 0;
}
}
Static Constructor:
A static constructor is used to initialize
any static data,
or to perform a particular action that needs to be performed once only.
It is
called automatically before the first instance is created or any static members
are referenced.
Static constructors are invoked only once and that
is before creation of first instance of
the class.
class SimpleClass
{
// Static variable that must be initialized at run time.
static readonly long baseline;
// Static constructor is called at most one time, before any
// instance constructor is invoked or member is accessed.
static SimpleClass()
{
baseline = DateTime.Now.Ticks;
}
}
Static constructors have the following properties:
C A static
constructor does not take access modifiers or have parameters.
C A static
constructor is called automatically to initialize the class before
the first instance is created or any static members are referenced.
C A static
constructor cannot be called directly.
C The user has
no control on when the static constructor is executed in the program.
Copy Constructor:
Unlike some languages, C# does not provide a copy
constructor.
If you create a new object and want to copy the values from an
existing object, you have to write the appropriate method yourself.
A parameterized constructor that contains a
parameter of same class type is called as copy constructor.
Main purpose of
copy constructor is to initialize new instance to the values of an existing
instance.
