Question

I have this code

 classObject var1 = new classObject();
 classObject var2 = var1;

Now, I wrote this:

 var1 = null;

How the GC will handle this ?
Does GC will collect the instance of this classObject ?

And how GC will hangle this if i will wrote var2= null ?
( and remove the var1=null from the code )

Answer 1

Short answer: no, because var2 still refers to the instance. As long as you have at least one reference to an object, the object will not be collected.

Longer answer: actually, probably it will in this example, because you don’t go on to do anything with var2. The GC takes variable liveness into account. If you never use var2 again in the code, var2 is considered not to be live after that last line of code there. And so such a reference is considered not to be meaningful for garbage collection purposes – it’s as though var2 no longer exists. So in fact, the object will be eligible for collection:

Additional subtleties: it will also depend on whether you’re running in debug or release mode. When debugging, .NET artificially extends the liveness of variables to extend to the end of their lexical scope, so that you have the opportunity to inspect local variables. Also, of couse, objects will only be collected when the GC actually runs.

So strictly speaking, it’s not actually possible to give on universally correct answer.