2

The documentation for finalize says

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

So I assumed that finalize method will be called on the object once the program execution ends.

public final class MainClass{


    public static void main(String[] args) {
        A s = new A(5);
        s = new A(6);
        System.out.println(s);

        System.out.println("End of main");
    }

}
final class A{

    private int value;

    public A(int value) {
        this.value = value;
    }

    @Override
    protected void finalize() throws Throwable {

        System.out.println("Destroyed object is :"+this);
        System.out.println("Inside finalize");
        super.finalize();
    }       

    @Override
    public String toString() {
        return ((Integer)value).toString();
    }
}

The output of the program is 

6
End of main

After the initialization of new A(6) with System.gc() then the finalize method is run and object with value 5 is removed by the garbage collector and the output will be 

6
Destroyed object is :5
Inside finalize
End of main

I have read that OS will clean up the memory once the program is over so there is no need for garbage collection when the program is running.

So I have three questions,

  1. Will finalize method be called with an object of type A() is garbage collected? If yes, then why was it not called now and If no, in which instances will it be called?
  2. Will finalize() method be called everytime an object is garbage collected?
  3. If garbage collection does not happen when the program is run, then will there be a jvm process trigger garbage collection long after the program completes?

NOTE: In my case, Garbage collector is called because new A(5) is no longer referenced in the program.

EDIT:

Explanation on why this question is different:

This question is more about will finalize() method always be called on garbage collection and can garbage collection occur without the invocation of the finalize() method.

Such a question has not been raised and if it has, an answer for such a question is not available on StackOverflow.

Naveen Dennis
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    1. Yes. Garbage collection is pointless at exit. The whole vm goes away. 2. No. Finalization is not guaranteed at exit time. 3. No. The operating system just gets the memory back; the jvm is just another process to the operating system. – Elliott Frisch Apr 04 '18 at 17:43
  • Garbage collection and finalization are two distinct actions. So even if an instance gets collected, there can be an arbitrary amount of time before its finalization and it’s perfectly possible that the JVM terminates in-between, so even if an object gets collected, there is no guaranty that it will ever get finalized. But as already said, the collection itself will only happen if the program is still running and needs more memory. It *may* happen when you call `System.gc()`. – Holger Apr 05 '18 at 11:19

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