1. Advanced Java Class Events

2. change in state initiated by system or user java.util.EventObject java.awt.event java.swing.event

3. Event flow of control Listener registers with object that emits events. –frame.addKeyListener( myKeyListener ) An object emits an event –for example, the user presses a key The JVM notifies all listeners registered with that object. –for example, the method public void keyPressed(KeyEvent e) in the myKeyListener object is called when a user presses a key. The Listener extracts information from the Event object and does something appropriate –for example, it queries the Event to find out which key was pressed, and then moves a frog in that direction.

4. Common AWT Events ActionEventA component such as a toolbar or menu item emitted an action event (i.e. “cut “) AdjustmentEventScrollbar moved ComponentEventComponent moved, resized, etc. ContainerEventcontents of container changed FocusEventcomponent gained or lost focus ItemEventselection changed in checkbox, list, etc. KeyEventkey pressed, released, or typed MouseEventmouse entered, exited, clicked, pressed, or released TextEventText edited WindowEventWindow opened, closing, closed, (de)activated, or (de)iconified

5. Common Swing Events ChangeEventVery general -- something changed ListSelectionEventA different item in a list was selected – emitted by ListSelectionModel, listened for by Jtable (& others) MenuEventA menu was selected, deselected, or canceled. TableModelEventSomething in a TableModel changed TreeSelectionEventA different path in a tree was selected – emitted by TreeSelectionModel

6. Listeners & Adapters Listeners register with objects that emit events, by calling a specific method: add[fillInType]Listener(thisListener) One Listener class per Event Class Adapters are simple classes that provide empty implementations of the methods. Use adaptors if you don’t want to implement all the methods in a listener interferer Some Adapters implement more than one Listener, and not all Listeners have Adapters

7. Example of Using Events component.addKeyListener(new KeyAdapter(){ public void keyTyped(KeyEvent e) { System.out.println("key typed“ +e.getKeyChar()); } });

8. ActionEvents

9. Actions Actions are a shortcut for ActionListeners They have names and (optionally) icons They can be added to tool bars and menu items. Example: JMenuItem crashItem = new JMenuItem(); crashItem.setAction(new AbstractAction() { public void actionPerformed(ActionEvent e) { Audio.crash(); } });

10. Actions and Events Task import javax.swing.*; import java.awt.event.*; import java.awt.*; import java.util.TimerTask; public class EventTask { private static ImageDisplayer displayer; public static void main( String[] args ){ JFrame frame = setUpFrame(); setUpMenuBar( frame ); setUpImageDisplayer( frame.getContentPane() ); frame.show(); } private static void setUpImageDisplayer( Container contentPane ) { /* fill in to put an instance of ImageDisplayer into the GUI */ } private static JFrame setUpFrame() { /* fill in set up a new 300 by 300 frame tell it to respond to a user pressing the letter f by asking the ImageDisplayer to briefly show it’s image. */ } private static void setUpMenuBar( JFrame frame ) { /* give the frame a menubar, with one menu, which should have one menu item the menu’s name should be “Image”, and the menu item’s name should be “Show Image” when the user selects the menu item, it should ask the ImageDisplayer to briefly show it’s image */ } static class ImageDisplayer extends JComponent { //use definition from GUI task }

11. Solution to task import javax.swing.*; import java.awt.event.*; import java.awt.*; import java.util.TimerTask; public class EventTask { private static ImageDisplayer displayer; public static void main(String[] args ){ JFrame frame = setUpFrame(); setUpMenuBar(frame); setUpImageDisplayer(frame.getContentPane()); frame.show(); } private static JFrame setUpFrame() { JFrame frame = new JFrame("Event Task"); frame.setSize(300, 300); frame.addKeyListener(new KeyAdapter(){ public void keyTyped(KeyEvent e) { if (e.getKeyChar() == 'f') { displayer.showImageBriefly(); } }); return frame; } private static void setUpMenuBar(JFrame frame) { JMenuBar menuBar = new JMenuBar(); JMenu menu = new JMenu("Image"); JMenuItem showImageItem = new JMenuItem(); showImageItem.setAction(new AbstractAction() { public void actionPerformed(ActionEvent e) { displayer.showImageBriefly(); } }); showImageItem.setText("Show Image"); menu.add(showImageItem); menuBar.add(menu); frame.setJMenuBar(menuBar); } private static void setUpImageDisplayer(Container contentPane) { displayer = new ImageDisplayer(); contentPane.add(displayer); } static class ImageDisplayer extends JComponent { // use defiinition from gui1 task }