What is animation? To put it simply, animation is the illusion of movement. When you watch television, you see lots of things moving around. You are really being tricked into believing that you are seeing movement. In the case of television, the illusion of movement is created by displaying a rapid succession of images with slight changes in the content. The human eye perceives these changes as movement because of its low visual acuity. The human eye can be tricked into perceiving movement with as low as 12 frames of movement per second. It should come as no surprise that frames per second (fps) is the standard unit of measure for animation. It should also be no surprise that computers use the same animation technique as television sets to trick us into seeing movement.
The bouncing ball animation (below) consists of these 6 frames.
This animation moves at 10 frames per second.
Although 12 fps is enough technically to make animation work, the animations sometimes look jerky. Most professional animations therefore use a higher frame rate. Television uses 30 fps, and motion pictures use about 24 fps. Although the number of frames per second is a good measure of the animation quality, it isn't always the bottom line. Professional animators have the ability to create their animations with a particular frame rate in mind so that they can alleviate some of the jerkiness at slower speeds.
When you program animation in Java, you typically have the ability to manipulate the frame rate a fair amount. The obvious limitation on frame rate is the speed at which the computer can generate and display the animation frames. There is usually some give and take between establishing a frame rate low enough to yield a smooth animation, while not bogging down the processor and slowing the system. You learn more about all that later. For now, keep in mind that when programming animation in Java, you are acting as a magician creating the illusion of movement for the users of your applet.
