Swing Hacks

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Chapter 12, Miscellany

#89 Fun with Keyboard Lights

HACK

And More...

The most obvious enhancement is to use real images for the cursor, as the

many cursor packs available on the Web can attest (type “free cursors” into

Google and see what you get). Animated cursors could also be used to indi-

cate other elements of program state, such as network traffic or the current

tool in use. With a few images and the help of the

setCursor( ) function, you

can do almost anything.

H A C K

#89

Fun with Keyboard Lights Hack #89

Flash the Caps Lock, Num Lock, and Scroll Lock keys for extra user

feedback.

The AWT and Swing APIs are huge and full of robust components and

frameworks for building big applications. They also have some dark corners

where the lesser-known functions live. While cruising through the JavaDoc

for

java.awt.Toolkit, I ran across a function I had never noticed before,

despite it being in the API for over four years. This hack explores building a

keyboard busy indicator using the

Toolkit.setLockingKeyState( ) function.

The root class of AWT,

Toolkit, has a very interesting little function:

setLockingKeyState( ). You pass it the KeyEvent for the key you want to lock

down and turn it on or off with the

boolean. For most keyboards, this means

the Caps Lock, Num Lock, and Scroll Lock keys (some keyboards may also

have a Kana lock for Kanji support). Now that you have this nifty little func-

tion, what should you do with it?

My first thought was a busy cursor. If you’ve got three lights in a row, why

not blink them off and on in sequence? The code in Example 12-2 will flip

each light on and off in order, creating a moving bar effect (depending on

the order of your keyboard LEDs).

Figure 12-1. An animated cursor

Fun with Keyboard Lights #89

Chapter 12, Miscellany

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447

HACK

SpinnerThread is a Runnable implementation, meaning you can launch it with

new Thread(new SpinnerThread()).start( ). The run( ) method starts an infi-

nite loop, ending only when the

quit( ) method is called. The first thing to

notice is that the code saves the existing state of the buttons so that it can

restore them later. If you had Caps Lock on you’d probably still want it on

once the busy cursor leaves. Next, it sets all of the key states to false. This

puts them into a known position so that the animation looks right:

int key = -1;

boolean state = false;

// loop through 100 times

int counter = 0;

while(go) {

// select each key every 3rd time

if(counter%3 == 0) { key = KeyEvent.VK_NUM_LOCK; }

if(counter%3 == 1) { key = KeyEvent.VK_CAPS_LOCK; }

if(counter%3 == 2) { key = KeyEvent.VK_SCROLL_LOCK; }

// flip the state

state = tk.getLockingKeyState(key);

tk.setLockingKeyState(key,!state);

// sleep for 500 msec

try { Thread.currentThread( ).sleep(500);

} catch (InterruptedException ex) {}

// increment counter

counter++;

}

Example 12-2. Lights, camera, action

class SpinnerThread extends Thread {

private boolean go;

public void quit( ) {

go = false;

}

public void run( ) {

go = true;

// get a toolkit

Toolkit tk = Toolkit.getDefaultToolkit( );

// save the old key states

boolean old_num, old_caps, old_scroll;

old_num = tk.getLockingKeyState(KeyEvent.VK_NUM_LOCK);

old_caps = tk.getLockingKeyState(KeyEvent.VK_CAPS_LOCK);

old_scroll = tk.getLockingKeyState(KeyEvent.VK_SCROLL_LOCK);

// set all keys to off

tk.setLockingKeyState(KeyEvent.VK_NUM_LOCK,false);

tk.setLockingKeyState(KeyEvent.VK_CAPS_LOCK,false);

tk.setLockingKeyState(KeyEvent.VK_SCROLL_LOCK,false);