CODEWITHSUNDEEP
c#
Himanshu Jain
Himanshu Jain

Reputation: 103

I am little confused between class, object and instance

I read a lot about difference between class,object and reference. But I have question in mind.So please help me in solving that. Suppose

Class A        //declaration of class
{
//
}

main()
{
    A s1 = new A();
    A s2 = new A();
}

Now Question is that In above code that how many there is different object and instance in the memory.?

If one says there is two different object and two instance (i.e s1 and s2) then if we change in one instance suppose s1 then it also reflects changes in s2 also. Which shows that there is only one object present in the memory.

So How can we made different objects in the memory of same class A?

Thanks in advance!!

Upvotes: 1

Views: 153

Answers (3)

Jason Evans
Jason Evans

Reputation: 29186

In your example code, there are 2 instances of class A in memory. s1 and s2 each point to a memory address where a A instance lives.

Using the words object and instance tend to mean the same thing, so you could use them interchangeably.

Now, if you did this:

main()
{
    A s1 = new A();
    A s2 = s1;
}

In that case, both s1 and s2 point to the same object/instance (same memory address). So if you made changes to either s1 or s2 then they would be reflected either way.

EDIT:

A little extra explanation...

main()
{
    A s1 = new A();  
}

In the above code, the variable s1 is instantiated to a new A instance. Two things have happened here

  • An instance of A has been created in the heap memory region.
  • s1 stores (on the stack) the memory address in the heap.

s1 will be created on the stack, and it is effectively a pointer to the memory address in the heap where the A instance has been created.

Hopefully this extra bit of info is helping to clarify things.

EDIT:

You can create as many instances as the memory on your PC will allow.

main()
{
    A s1 = new A();
    A s2 = new A();
    A s3 = new A();
    // etc until you run out of memory.
}

I strongly suggest you look at buying some books to help you grasp the fundamentals of .NET programming. My favorite book, and one I turn to a lot, it CLR via C# 4th Edition. You can't go wrong with that book.

Upvotes: 1

chiccodoro
chiccodoro

Reputation: 14716

As opposed to your statement, "if we change in one instance suppose s1 then it also reflects changes in s2 also", the changes in s1 will not reflect in s2. Hence there are two instances in memory.

You could possibly be confused because a class can contain a property or field which is a reference to yet another object. Then you can perfectly reference the same object in both s1 and s2:

s1.s3 = new B();
s2.s3 = new B();

In that case of course, changing anything in s1.s3 will reflect in s2.s3.

As for the title of your question, an Object is an Instance of a Class.

Upvotes: 1

Ojonugwa Jude Ochalifu
Ojonugwa Jude Ochalifu

Reputation: 27256

According to the MSDN website:

An object is basically a block of memory that has been allocated and configured according to the blueprint. A program may create many objects of the same class. Objects are also called instances, and they can be stored in either a named variable or in an array or collection

Objects and instances are the same thing, and they belong to a class (are created from classes) by your code, you have created two objects in memory, and the variables s1 and s2 are references to these objects.

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Image Source

Upvotes: 1

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