NP62 Method call

Hi Alan

Nowadays rarely see in the forum. Thank you for your explanation.

Hi Maha,

The following line throws an exception:

DisplayStrings("Thomas", new John());

because there's no conversion defined between an object of type John and string which is required by the foreach() statement in the DisplayStrings method.

If you were to change the John class to this:

class John
{
   public override string ToString()
   {
      return "John";
   }  
}

and the foreach statement to this:

foreach (object person in people)
   Console.Write("{0} ", person);

then there'd be no exception because:

1. The conversion to string is no longer needed because the person variable is now of type object rather than string.

2. When an object is used in a call to Console.Write (or WriteLine), then the underlying code looks to see whether the object overrides the ToString() method and, if it does, uses the value returned by that method. If it doesn't override it, then the name of the type itself would be printed. So, even if you commented out the ToString() method, "John" would still get printed out here :)
 

The following program will executing after declearing empty class John because  new John() is used in the program. I wish to know the reason for that. Please explain.

using System;

class John

{}

public class ParamsDemo

{

    public static void Main()

    {

        string[] names = { "Mark", "Paulette", "Carol", "James" };

        DisplayStrings("Ginger"); // one string argument

        DisplayStrings("George", "Maria"); // three string argument

        DisplayStrings(names); // array of string

        DisplayStrings("Thomas", new John());

    }

    public static void DisplayStrings(params object[] people)

    {

        foreach (string person in people)

            Console.Write("{0} ", person);

        Console.WriteLine("\n-------------------");

    }

}

/*

Ginger

-------------------

George Maria

-------------------

Mark Paulette Carol James

-------------------

Thomas

*/

Now matter is clear thank you for your explanation, Satish Kumar Kathi

In your program object type is "parameter array of object"

public static void Test(string sister, params object[] papers)

Alan also said the same

“So in this example we actually have a parameter array of objects which means we can pass any number of arguments of any type such as Paper and NonPrintablePaper and the compiler will be quite happy.”

In your program object type is declared I agreed with that in my program where is the object type declaration?

One can say new Emp("1", "First Name", "Last Name")  is equal to anything which will become an object after declearation of type.  

According to you new Emp("1", "First Name", "Last Name")  is only equal to object “objEmp”

So then what is the type of objEmp?

That mean you say “Emp objEmp” is automatically created when you declare EmployeeFullname(new Emp("1", "First Name", "Last Name"));. Which I won’t agree

in my view new Emp("1", "First Name", "Last Name")  is only equal to object “objEmp” where is the declearation of type?    

What you said is correct, I will try

Here is sample code

public string EmployeeFullname(Emp objEmp)

        {

            string fullname = objEmp.LName + "," + objEmp.FName;

            return fullname;

        }

        private void button5_Click(object sender, EventArgs e)

        {

            EmployeeFullname(new Emp("1", "First Name", "Last Name"));

        }

According to you EmployeeFullName accepts Emp object so you want to create object and pass it

Like

 Emp objEmp = new Emp("1", "First Name", "Last Name");

If you see my code above the left part “Emp objEmp”  is created in the method signature public string EmployeeFullname(Emp objEmp)

And the right part “new Emp("1", "First Name", "Last Name");”  creating an object is done when you are calling the method “EmployeeFullname(new Emp("1", "First Name", "Last Name"));” 

In either way you are doing the same

You are declaring variable in method and allocating memory when you are calling the method

A two-step process creates an object that is an instance of a class.

First, you supply a type and an identifier, just as when you declare any variable. Second, you allocate computer memory for that object.

Here in the above program new Paper()and new NonPrintablePaper()are not created according to rule. That means according to rule below is the perfect way of creating an instance of a class.  

Paper print = new Paper();

NonPrintablePaper nonprintablepaper = new NonPrintablePaper()

But without this program is executing well. Anyone knows please explain the reason.

Hi Maha,

The following advice is a bit loose:

"When you call the method, however, the arguments you send to it must match in both number and type with the arguments listed in the method declaration."

In practice the arguments have either to be of the same type as, or of a type which is implicitly convertible to, the parameter type.

This means that, if you have a parameter of type 'object', then you can pass an argument of any type to the method in respect of that parameter because all types are implicitly convertible (i.e. a cast is not needed) to 'object'.

So in this example we actually have a parameter array of objects which means we can pass any number of arguments of any type such as Paper and NonPrintablePaper and the compiler will be quite happy.