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Index › Programming Questions & Help › Syntax Questions › How do objects in an ArrayList get status updates
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How do objects in an ArrayList get status updates? (Read 494 times)
NoChinDeluxe
How do objects in an ArrayList get status updates?
May 27th, 2009, 9:34am  
This is just a curiosity question. If I have code looking something like this:

Code:

ArrayList things = new ArrayList();
things.add(new Thing());
Thing thing = (Thing)things.get(i);
thing.doStuff();


I've noticed that you don't have to include Code:
things.set(0,thing);
at the end to update your original object in the ArrayList with the local object you just messed with. Your original object in the ArrayList is simply updated accordingly. I never quite understood why that happens. It's about time I find out.  Wink Can someone fill me in?
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Blaine
Re: How do objects in an ArrayList get status updates?
Reply #1 - May 27th, 2009, 9:46am  
The reason you don't have to set the value is because the array itself doesn't actually hold the objects. It holds a reference to the object. A shortcut, if you will. If the 3rd item in an array is an object called Ball, then

blargle = (Thing)things.get(3);
blargle.x = 10;

is the same as just inputing

Ball.x = 10;

Now for this example you're updating an x field, which will be used during your draw() loop or something.

But the point is, you don't have to use set() for the arraylist for the same reason you don't have to use set() for Dude.x = sin(mouseX);

I think that's your question... if not, ignore me.
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NoChinDeluxe
Re: How do objects in an ArrayList get status updates?
Reply #2 - May 27th, 2009, 9:56am  
No, that's perfect. Thanks for the reply. I should have realized myself that it's a reference. Kind of like vectors in C++.
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