Object Data Type

Question

In the following program if data type is object, GetType() method returning data type is assigned value data type.

If object obj4 = new object(); then only returning data type is System.Object.What is the reason for that?

using System;

namespace ConsoleApplication2
{
class Program
{
static void Main(string[] args)
{
int value = 5;
object obj1 = 12;
object obj2 = "Scarborough";
object obj3 = 'A';
object obj4 = new object();

Console.WriteLine(value.GetType());
Console.WriteLine(obj1.GetType());
Console.WriteLine(obj2.GetType());
Console.WriteLine(obj3.GetType());
Console.WriteLine(obj4.GetType());

Console.ReadKey();
}
}
}

/*
System.Int32
System.Int32
System.String
System.Char
System.Object
*/

Maha · Answer

Thank you for additional information.

Vulpes · Answer

Incidentally it's the fields of the class which will have all their bytes set to zero. This is why if you don't give them an explicit value fields have the following values by default: numeric value types - 0 bool - false char - '\0' all reference types - null because these values correspond to 'all bytes zero'. The Employee class doesn't actually have any fields and so you'd expect on the face of it that it wouldn't require any memory to be allocated on the heap. However all objects have some overhead (at least 8 bytes) and if there are no fields the CLR will allocate a minimum of 1 byte memory as a place-holder because there needs to be an address where the fields would otherwise start for technical reasons.

Maha · Answer

Thank you for your explanation.

Vulpes · Answer

If you pass Console.WriteLine something which isn't a string (such as 'myAssistant') then it applies the ToString() method to it before printing the result to the console. Unless it is overridden in the Employee class the ToString() method will simply return the name of the type i.e. 'Employee' here.

Maha · Answer

If all the bytes of the memory is set to zero why myAssistant returning value is not zero but Employee. Problem is highlighted. using System; namespace ConsoleApplication2 { class Program { static void Main(string[] args) { int myInteger = new int(); Employee myAssistant = new Employee(); Console.WriteLine(myInteger); Console.WriteLine( myAssistant ); Console.ReadKey(); } } } class Employee { } /* 0 Employee */

Vulpes · Answer

You're correct that in the case of a class such as Employee the 'new' operator causes memory to be allocated on the heap and all the bytes of that memory to be set to zero. A reference (or pointer) to this memory is then assigned to the variable concerned (myAssistant in your example). However in the case of a struct such as int (System.Int32) the variable (myInteger in your example) contains the struct itself not a reference to it. The role of the 'new' operator in relation to a struct is therefore not to allocate memory but to set all the bytes of the variable containing it to zero. So this line: int myInteger = new int(); causes all 4 bytes of the 'int' variable myInteger to be set to zero which has the effect of giving myInteger a value of 0. In other words it's exactly equivalent to this line: int myInteger = 0; which is usually preferred in practice.

Maha · Answer

When declaring like Employee myAssistant = new Employee (); 1.You are notifying the compiler that you will use the identifier myAssistant. 2. new operator is allocating computer memory. When declaring like int myInteger = new int (); Please tell me what will happen behind the screen.

Vulpes · Answer

The Object.GetType() method returns the actual type of the instance which the object variable refers to. Clearly: obj1 refers to an int (or System.Int32) obj2 refers to a string (or System.String) obj3 refers to a char (or System.Char) and obj4 refers to an object (or System.Object) because a new object is created and then a reference to it is assigned to obj4.