[edit] How to use C# constructors
When you use the new operator it may be necessary to initialize field values to custom values. It is not necessary to define a C# constructor a default constructor is called if there are no programmer defined constructors. The default constructor does not do anything except creates your object.
- A constructor is a method that has the same name as the class name
Lets take a look at how to define a constructor of our own.
using System;
class Program
{
public class test
{
public int testvariable;
public test(int test) //Constructor
{
this.testvariable = test;
}
}
static void Main()
{
test ClassObject = new test(81); //call constructor
//print class field member
Console.WriteLine(ClassObject.testvariable);
Console.Read();
}
}
Output:
81
- public test(int test) has the same name as the class and it does not specify a return type because constructors do not return values.
- new test(81); calls the constructor and the constructor simply assigns the field member to its local variable.
[edit] How to Overload C# Constructors
Just like C# functions and methods, constructors can be overloaded too. There my be different situations where you may have two different situations and need two different constructors.
- You must match parameters when using constructors
- You can have as many constructors as you need
Lets take a look at an example:
using System;
class Program
{
public class test
{
public string testvariable;
public test() //Default Constructor
{
this.testvariable = "John Doe";
}
public test(string test) //Overloaded Constructor
{
this.testvariable = test;
}
}
static void Main()
{
test ClassObject = new test(); //call default constructor
test ClassObject2 = new test("Jeannette"); //call constructor
//print class field member
Console.WriteLine(ClassObject.testvariable);
Console.WriteLine(ClassObject2.testvariable);
Console.Read();
}
}
Output:
John Doe
Jeannette
[edit] C# Copy Constructor
When writing your C# application you may need to copy class objects to other class objects. To do this you need a copy constructor because there is no build in way to do this. The copy constructor simply copies all the field values of the right side to the left side.
Call a copy constructor like this:
test ClassObject2 = new test(ClassObject);
- the new keyword must be used to call the copy constructor
- The parameter to pass to the constructor must be the value of the leftside object
Lets take a look at example code:
using System;
class Program
{
public class test
{
public string testvariable = "";
public test(string test) //Constructor
{
this.testvariable = test;
}
public test(test leftside) //Copy constructor
{
this.testvariable = leftside.testvariable;
}
}
static void Main()
{
test ClassObject = new test("Elaine"); //create first object
test ClassObject2 = new test(ClassObject); //Call copy constructor
//print class field member
Console.WriteLine(ClassObject.testvariable);
Console.WriteLine(ClassObject2.testvariable);
Console.Read();
}
}
Output:
Elaine
Elaine
Note: you can only copy objects that are created from the same class
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