Why is finalize not being called?

There is a lot to finalize() method which is frankly a lot to write, but in short:

An object is in the finalized state if it is still unreachable after its finalize method, if any, has been run. A finalized object is awaiting deallocation. Note that the VM implementation controls when the finalizer is run. You are almost always better off doing your own cleanup instead of relying on a finalizer. Using a finalizer can also leave behind critical resources that won't be recovered for an indeterminate amount of time.

In your case the reason it does not print is that you do not know when the finalizer thread will call the finalize() method. What is happening is that the program is terminating before anything can get printed. To check it: edit the code inside main code by( NOTE: this does not guarrantee nor should you should ever rely on it but still it does prints some time)

for(int i =0;i<1000000;i++)
    {
        MultipleConstruct construct = new MultipleConstruct(3);
        construct = null;
    }

There are a lot of disadvantages of using a finalize() right from taking more time in object construction to possibility of memory leakage and memory starvation. If you strongly refer to the same object inside the finalize() then it is never called the second time and thus can leave system in undesired state etc etc etc... The only place where you should use finalize() is as a safety net to dispose any resources like InputStream uses it to close (which again there is no guarrantee that it will will br run when your program is still alive). Another place to use it is while using natives where garbage collector has no control.

For more info visit:

http://jatinpuri.com/?p=106

q1) finalize method is called when the object is being garbage collected, thus, if no GC is being performed, your finalizer may not be called. You need to call super simply to preserve the behavior provided by Object implementation.

q2) the exact moment in which GC is performed depends on a lot of factors like: which JVM you are using, tuning parameters, amount of free heap, etc. So it does not only rely on a used heap threshold. You can also ask for a GC to be performed through System.gc() but you have no guarantee about if and when it will be actually executed. You can find some details on how to configure GC in http://java.sun.com/performance/reference/whitepapers/tuning.html

it gets called eventually or not at all

basically the GC scans the heap for everything that is not reachable and runs the finalizer on those (after which it needs to prove again it is not reachable for it to be freed)

however it can take a while (effectively undefined and actually dependent on program behavior) for the GC to find it which is why you shouldn't really rely on it to dispose of critical data

edit: as for circular references it distinguishes between objects with a finalize method and objects without one

for an object to be freed (deleted from main memory) it may not be reachable by any code (this includes finalizers that still need to run)

when 2 objects with finalizers are eligible to get the finalizers run the GC arbitrarily selects one object and runs the finalizer on it and then it can run the other object

note that a finalizer can run while the fields of the objects may or may not be finalized already