what happens to the value returned by 'createBufferStrategy'?

Question

I'm learning about BufferStrategy and I'm kind of confused with the creation of BS.

my code looks like this...

public class Game extends Canvas{


    /*code not relevant to this topic..
                                       */



    public void render(){
        BufferStrategy bs = this.getBufferStrategy();
        if(bs == null){
             createBufferStrategy(3);
        }
    }

}

basically, my class 'Game' is a subclass of Canvas.. and that class get's the buffer strategy and stores it in bs.

However, bs did not "create" a buffer strategy and if it is null (which in this case it is), i say "createBufferStrategy(3)".

I'm confused as to what happens when I createBufferStrategy(3) or this.createBufferStrategy(3) (which is the same thing).

Where exactly is the value of createBufferStrategy(3) stored?

It cannot be stored in bs.. so how does bs go from null to actually being initialized or holding a value when I only told my subclass to create a buffer strategy. I don't see how I changed the state of bs from null to whatever..

I tried to do bs = createBufferStrategy(3) and it doesn't work, obviously. I'd like to know why and how and what exactly is happening.

Thank you in advance.

have a look at the api docs http://docs.oracle.com/javase/6/docs/api/java/awt/Canvas.html#createBufferStrategy(int), the BufferStrategy is created in the `Component` — htz, Jul 04 '13 at 07:09
Could you post more of `render`? I guess you only posted part of it. — johnchen902, Jul 06 '13 at 08:47

MadProgrammer · Accepted Answer · 2013-07-11T08:29:30.197

2

From the JavaDocs

public BufferStrategy getBufferStrategy()

Returns the BufferStrategy used by this component. This method will return null if a BufferStrategy has not yet been created or has been disposed.

By default, Canvas does not create or use any type of buffer strategy. In your code, when you call

BufferStrategy bs = this.getBufferStrategy();
if(bs == null){

You are checking to see if any previous buffer strategy has being create and is active (hasn't being disposed), this ensures that when ever this method is called, all attempts are made to provide a valid BufferStrategy

When you call createBufferStrategy(3); it constructs a BufferStrategy internally to meet your requirements and assigns the results back to an internal instance variable, which is returned by calling getBufferStrategy

You might try changing your code to something more like...

BufferStrategy bs = this.getBufferStrategy();
if(bs == null){
    createBufferStrategy(3);
    bs = this.getBufferStrategy();
}

if (bs == null) {
    // It might not be possible to create a buffer strategy for your hardware,
    // or the component is not attached to a native peer
} else {
    // Start painting :D
}

edited Jul 11 '13 at 08:29

answered Jul 10 '13 at 01:46

MadProgrammer

343,457
22
230
366

See also this [_Invaders_](http://www.cokeandcode.com/index.html?page=tutorials/spaceinvaders101) tutorial. – trashgod Jul 10 '13 at 09:49
very good explenation, I understand it really well now, thanks :) – Space Ghost Jul 11 '13 at 21:18
1

When calling getBufferStrategy we retrieve an instance of the Buffer Strategy, but what does it actually returns? Does it holds only one instance to the current buffered image we going to work on, out of the three? – homerun Dec 22 '15 at 19:37
1

Essentially, yes, the internal mechanism is maintaining a reference to the "working" buffers and the "display" buffer, so you're guaranteed not get the "display" buffer – MadProgrammer Dec 22 '15 at 20:13

score 1 · Answer 2 · answered Jul 09 '13 at 21:58

You initialized the BufferStrategy bs to that components BufferStrategy (this.getBufferStrategy). I don't know too much about the inner workings, but I have and am using this currently for my game. This is used mainly for buffering images to be displayed(i.e. in a game) you would be calling getBufferStrategy every time you're painting to the screen, so bs is just a reference. You could just as well write:

if(this.getBufferStrategy() == null)

So what I'm saying is that the BufferStrategy is created in the component and checking whther it is null is probably just to prevent an error at the program's start because I don't think there is a BufferStrategy until you manually create it.

what happens to the value returned by 'createBufferStrategy'?

2 Answers2