Shouldn't this object be garbage collected ?

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i learned in Java that if an object doesn't have any reference to it, it will be garbage collected automatically, but why the object below works fine and doesn't have any reference to it, shouldn't it be garbage collected?

Java

public class Main {

    public static void main(String[] args) {
	new A().show();
    }
}


class A{
    void show(){
        System.out.println("Java");
    }
}

What I have tried:

there was nothing i could try!

Posted 25-Apr-19 5:06am

hiwa doski

Updated 25-Apr-19 5:22am

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[no name] 25-Apr-19 11:11am

Your comments bear no relation to what you're showing. You're showing an apple while commenting about the taste of oranges.

hiwa doski 25-Apr-19 12:30pm

if garbage collector is not related to this then i don't know what is ?

Richard MacCutchan 25-Apr-19 12:36pm

Look at your code. You create a new object of the A class and call its Show method. You then terminate your application. So how do you know the garbage collector was never called?

hiwa doski 25-Apr-19 12:49pm

i thought the garbage collector will immediately start and remove it, but it turned out that I was wrong.

Richard MacCutchan 25-Apr-19 12:56pm

I ask again: how do you know that it didn't?

hiwa doski 25-Apr-19 13:07pm

because the method got executed!

Richard MacCutchan 25-Apr-19 13:32pm

Of course it got executed, that is what the call to the Show method is supposed to do.

hiwa doski 25-Apr-19 16:08pm

and i thought if it got garbage collected it wasn't gonna get executed, so that's why i said it didn't got garbage collected.

Richard MacCutchan 26-Apr-19 4:21am

It cannot get garbage collected until all references are removed. When the object is created in main (as a temporary object) it has a reference. It then calls the Show method which prints the string. On return from Show, there is no more code in main, so the object goes out of scope and its destructor is called. There are now no longer any references to the object so it can be garbage collected. But as the application now terminates the garbage collector will not be necessary.

hiwa doski 26-Apr-19 4:42am

That's a very good explanation, thanks.

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OriginalGriff · Accepted Answer · 2019-04-25T05:22:00

Solution 1

Why would a garbage collector be called in when your app exits? It's a load easier to just release all memory as a lump without worrying about disposing of each individual object - the app is dying, so just release all allocated memory back to the system instead.

And do remember that the garbage collector doesn't fire up immediately anything goes out of scope - it will wait until it's actually needed or the system is idle before it starts checking to see if anything is releasable. In your example the system is never idle until the app exits, and by that stage, it's too late for the GC to start work!

Posted 25-Apr-19 5:22am

OriginalGriff

Comments

hiwa doski 25-Apr-19 11:29am

what you mean by "when your app exits"

Richard Deeming 25-Apr-19 11:37am

When the main method ends, your application exits.

OriginalGriff 25-Apr-19 11:45am

Hard to believe anyone could get this far without realising that, isn't it?

Richard Deeming 25-Apr-19 11:45am

You must be new here! :D

OriginalGriff 25-Apr-19 12:05pm

Johnny-come-lately, that's me! :laugh:

hiwa doski 25-Apr-19 12:22pm

yeah i know, but i thought it will happen before that.

Richard Deeming 25-Apr-19 12:33pm

You've not exactly left it much time! :)

The GC typically runs when your application is running low on memory. You've only allocated a single tiny object, so you're not going to trigger it.

And your application exits almost immediately, so there wouldn't be any point in collecting the garbage anyway.

hiwa doski 25-Apr-19 13:08pm

Okay, thanks for your explanation.