do new in loop deletes old objects?

Question

Sorry for such simple questions but I am new in Java (usualy write in c)

do new in loop delete old instance of an object?

I need something like

   for(;;)
   {

     // work on here pixels[] 

     source = new MemoryImageSource(200, 200, pixels, 0, 50);
     image  = createImage(source;

    // then use image here

   }

I just need to get here above, new wraping of source and image objects in every frame, and do not want to bother of deleting it, But also I do not want to store large amounts of them as a memory leak,
Will it be deleted automatically? Is it heavy operation?

You can't delete things in Java anyway. You may just queue them for garbage collection. — auselen, Nov 28 '12 at 07:24
each object not referenced anymore will be clean by GC, though it's not always done at once. — Romczyk, Nov 28 '12 at 07:28
(@perception - to much reediting here on my post as to my opinion, i would not say that above) — grunge fightr, Nov 28 '12 at 08:22
Feel free to roll back the edit, thats the point of a collaborative wiki! — Perception, Nov 28 '12 at 08:24
editing is not bad (My english is not to much good - but i feel here it was to much of it, I do not find i was writing it such way) — grunge fightr, Nov 28 '12 at 08:32

score 5 · Accepted Answer · answered Nov 28 '12 at 07:30

5

Yes, objects that are no longer being referenced will be garbage collected automatically (at an unspecified point in the future).

I would recommend moving the declaration of source and image into the loop:

for(;;) {
  ...
  Source source = new MemoryImageSource(200, 200, pixels, 0, 50);
  Image image  = createImage(source);
  ...
}

Not only this is preferable stylistically, it also avoids keeping the last iteration's objects around for longer than necessary.

answered Nov 28 '12 at 07:30

NPE

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it’s bad style to declare and initialize objects inside a loop, you consume more resources this way....it’s better to declare them inside methods and when the method is out of scope the objects get cleaned up – firephil Nov 28 '12 at 19:18
@firephil: The whole point of the question is that there is a new pair of objects on every iteration. – NPE Nov 28 '12 at 19:20
my point is that you can reuse one reference instead say 1000 references if the loop runs 1000 times. Your way every time you loop you alocate new references Source,Image and new Objects Source,Image but you dont have to alocate new references for every iteration just new objects. – firephil Nov 29 '12 at 09:03

score 2 · Answer 2 · answered Nov 28 '12 at 07:28

2

No, creating and assigning a new instance to a variable in a loop does not 'delete' the old instance it was pointing too. However, as long as there are no other references to the instance it becomes eligible to be garbage collected.

answered Nov 28 '12 at 07:28

Perception

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will it make troubles? or could it be used? If not what other way can I do it? – grunge fightr Nov 28 '12 at 07:32
You should be fine, as long as your holding on to the `source` instance somewhere else in your code (for example, in your `createImage` function). – Perception Nov 28 '12 at 07:34

score 1 · Answer 3 · answered Nov 28 '12 at 07:39

GC is the basic difference between JAVA and C++. Java developers don't need to care about deleting instances any more and GC mechnism will delete it automatically once the instance is not referenced any more. for example, for (int i =0;i < 2;i ++){ source = new MemoryImageSource(200, 200, pixels, 0, 50); } in the loop,actually, 2 instances are created. But only the second instance is referenced by source after the loop. So the first instance is eligible to be garbage collected.

score 1 · Answer 4 · edited May 23 '17 at 12:18

1

Java behavior inside loop may be rather wierd. See Marko Topolnik's explanation of Java OutOfMemoryError strange behaviour

edited May 23 '17 at 12:18

Community

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answered Nov 28 '12 at 07:59

Evgeniy Dorofeev

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firephil · Answer 5 · 2014-07-23T12:06:52.673

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I would say the most efficient is the following :

Image image;

for(;;) {

    image  = createImage(new MemoryImageSource(200, 200, pixels, 0, 50));
  ...
}

You remove one unnecerary reference which builds up if you use a lot of them and you reuse the Image image reference instead of allocating memory in every iteration for the reference.

edited Jul 23 '14 at 12:06

answered Nov 28 '12 at 08:22

firephil

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do new in loop deletes old objects?

5 Answers5