edu.neu.ccs.gui
Class KeyPressReleaseListener

java.lang.Object
  edu.neu.ccs.gui.KeyPressReleaseListener

All Implemented Interfaces:

EventListener, KeyListener

public class KeyPressReleaseListener

extends Object

implements KeyListener

The class KeyPressReleaseListener implements a KeyListener that tracks the pressed-released state of keyboard keys. It is possible to track all key codes from the Java class KeyEvent or to supply a list of which particular key codes to track.

This class makes a best effort to track multiple simultaneous key press situations. We know however that in some cases the hardware does not deliver the required information to Java if "too many" keys are pressed. Let us explain.

We have run experiments using a laptop with an external USB keyboard attached. Here are some of the problems encountered.

• Some key combinations entered using the laptop keyboard are detected but the same key combinations entered from the external keyboard are not detected.
• In tests for the 36 keys 0-9 and A-Z, we have found that up to 6 keys pressed at once on the laptop keyboard can be detected but if a 7th key is pressed then it is not detected until one of the first 6 keys is released.
• In the same test using the external keyboard, the situation is much worse. If 6 keys are pressed then Java receives events that signal that all keys are released. This is a very disconcerting bug.

The bottom line is that software cannot process what the hardware and operating system refuse to deliver as proper and timely events.

Despite these significant issues, we felt that KeyPressReleaseListener is a valuable class for certain student software projects so we have decided to include it in JPT as is.

Since:

2.5.0

Version:

2.5.0

Field Summary

private BooleanStateArray

bsa The structure to maintain the pressed-released state.

Constructor Summary

KeyPressReleaseListener()
Initializes the internal state structure with all key codes from the KeyEvent class.

KeyPressReleaseListener(int[] list)
Initializes the internal state structure with the given list of key codes which should be a subset of the KeyEvent class key codes.

Method Summary

boolean	getState(int keycode) Returns the boolean state of the given key where true = pressed and false = released.
void	keyPressed(KeyEvent e) Stores the event key code state as true.
void	keyReleased(KeyEvent e) Stores the event key code state as false.
void	keyTyped(KeyEvent e) Does nothing.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

bsa

private BooleanStateArray bsa

The structure to maintain the pressed-released state.

Constructor Detail

KeyPressReleaseListener

public KeyPressReleaseListener()

Initializes the internal state structure with all key codes from the KeyEvent class.

KeyPressReleaseListener

public KeyPressReleaseListener(int[] list)

Initializes the internal state structure with the given list of key codes which should be a subset of the KeyEvent class key codes.

Parameters:

list - the list of key codes to track

Method Detail

keyPressed

public void keyPressed(KeyEvent e)

Stores the event key code state as true.

Specified by:

keyPressed in interface KeyListener

Parameters:

e - the KeyEvent sent to this listener

keyReleased

public void keyReleased(KeyEvent e)

Stores the event key code state as false.

Specified by:

keyReleased in interface KeyListener

Parameters:

e - the KeyEvent sent to this listener

keyTyped

public void keyTyped(KeyEvent e)

Does nothing.

Specified by:

keyTyped in interface KeyListener

getState

public boolean getState(int keycode)

Returns the boolean state of the given key where true = pressed and false = released.

Returns false if the key was not given in the list provided to the constructor since that key is not being tracked.

Parameters:

keycode - the keycode whose pressed-released state is being queried