BufferStrategy and BufferCapabilities
Trail: Bonus
Lesson: Full-Screen Exclusive Mode API

BufferStrategy and BufferCapabilities


In Java 2 Standard Edition, you don't have to worry about video pointers or video memory in order to take full advantage of either double-buffering or page-flipping. The new class java.awt.image.BufferStrategy has been added for the convenience of dealing with drawing to surfaces and components in a general way, regardless of the number of buffers used or the technique used to display them.

A buffer strategy gives you two all-purpose methods for drawing: getDrawGraphics and show. When you want to start drawing, get a draw graphics and use it. When you are finished drawing and want to present your information to the screen, call show. These two methods are designed to fit rather gracefully into a rendering loop:

BufferStrategy myStrategy;

while (!done) {
    Graphics g = myStrategy.getDrawGraphics();

Buffer strategies have also been set up to help you monitor VolatileImage issues. When in full-screen exclusive mode, VolatileImage issues are especially important because the windowing system can sometimes take back the video memory it has given you. One important example is when the user presses the ALT+TAB key combination in Windows--suddenly your full-screen program is running in the background and your video memory is lost. You can call the contentsLost method to find out if this has happened. Similarly, when the windowing system returns your memory to you, you can find out using the contentsRestored method.


As mentioned before, different operating systems, or even different graphics cards on the same operating system, have different techniques available at their disposal. These capabilities are exposed for you so that you can pick the best technique for your application.

The class java.awt.BufferCapabilities encapsulates these capabilities. Every buffer strategy is controlled by its buffer capabilities, so picking the right ones for your application is very crucial. To find out what capabilities are available, call the getBufferCapabilities method from the GraphicsConfiguration objects available on your graphics device.

The capabilities available in Java 2 Standard Edition version 1.4 are:

To create a buffer strategy for a component, call the createBufferStrategy method, supplying the number of buffers desired (this number includes the primary surface).  If any particular buffering technique is desired, supply an appropriate BufferCapabilities object. Note that when you use this version of the method, you must catch an AWTException in the event that your choice is not available. Also note that these methods are only available on Canvas and Window.

Once a particular buffer strategy has been created for a component, you can manipulate it using the getBufferStrategy method. Note that this method is also only available for canvases and windows.

Programming Tips

Some tips about using buffer capabilities and buffer strategies:

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