14.17. Key Event Handling

This section presents the KeyListener interface for handling key events. Key events are generated when keys on the keyboard are pressed and released. A class that implements KeyListener must provide declarations for methods keyPressed, keyReleased and keyTyped, each of which receives a KeyEvent as its argument. Class KeyEvent is a subclass of InputEvent. Method keyPressed is called in response to pressing any key. Method keyTyped is called in response to pressing any key that is not an action key. (The action keys are any arrow key, Home, End, Page Up, Page Down, any function key, etc.) Method keyReleased is called when the key is released after any keyPressed or keyTyped event.

The application of Figs. 14.36–14.37 demonstrates the KeyListener methods. Class KeyDemoFrame implements the KeyListener interface, so all three methods are declared in the application. The constructor (Fig. 14.36, lines 17–28) registers the application to handle its own key events by using method addKeyListener at line 27. Method addKeyListener is declared in class Component, so every subclass of Component can notify KeyListener objects of key events for that Component.