Pravin Yannawar, DOCS, NMU Jalgaon

Basic Java : Event handling in AWT and Swing 2 Objectives of This Session Explain the Event handling mechanism & demonstrate it using example List the categories of Events & Listener interfaces Demonstrate the above example using an independent event handler class Identify the need for adapter classes & demonstrate it using an independent event handler example

Basic Java : Event handling in AWT and Swing 3 Event Handling GUI applications are event-driven applications. They generate events when the user of the program interacts with the GUI. The underlying OS is constantly monitoring these events. When a event occurs, the OS reports these events to the programs that are running. The application will handle the event using a appropriate “Event Handler”.

Basic Java : Event handling in AWT and Swing 4 Delegation Event Model Source generates an event & sends it to one or more listeners. Listener simply waits until it receives an event. Once received, listener processes the event & returns.  Advantage : application logic that processes event is clearly separated from the UI logic that generates those events.  An UI element is able to delegate the processing of an event to a separate piece of code ( Event handler)

Basic Java : Event handling in AWT and Swing 5 Delegation Event Model Event: is an object that describes a state change in a source. Event Source: is an object that generates an event.  A source must register listeners for listeners to receive notifications about a specific type of event. Event Listener : is an object that is notified when an event occurs.  It must be registered with a source.  It must implement methods to receive & process these notifications.

Basic Java : Event handling in AWT and Swing 6 Event Handling import java.awt.*; import java.awt.event.*; class MyFrame extends Frame implements ActionListener { TextField t1; Button b1; MyFrame() { t1 = new TextField(20); b1 = new Button(“Click”); add(t1,”North”); b1.addActionListener(this); add(b1,”South”); }

Basic Java : Event handling in AWT and Swing 7 Event Handling public void actionPerformed( ActionEvent e ) { t1.setText(“Click pressed”); } public static void main(String args[]) { Frame f = new MyFrame(); f.setSize(100,100); f.show(); }

Basic Java : Event handling in AWT and Swing 8 Inheritance diagram of the AWT Event Classes Event Object AWT Event Component Event Action Event Adjustment Event Item Event Text Event Input Event Container Event Focus Event Paint Event Window Event Mouse Event Key Event

Basic Java : Event handling in AWT and Swing 9 Event Listener Interfaces ActionListener AdjustmentListener ComponentListener FocusListener ItemListener MouseListener MouseMotionListener KeyListener TextListener WindowListener ContainerListener java.util.EventListener

Basic Java : Event handling in AWT and Swing 10 Event Handling Summary InterfaceMethodsParameterEvents Generated by ActionListneractionPerformedActionEvent getActionCommand getmodifiers Button List MenuItem TextField Adjustment Listner adjustmentValue Changed AdjustmentEvent getAdjustable getAdjustmentType getvalue Scrollbar ItemListneritemStateChangedItemEvent getItem getItemSelectable getstateChange Checkbox CheckboxMenu Item Choice List TextListnertextValue ChangedTextEventTextComponent

Basic Java : Event handling in AWT and Swing 11 Event Handling Summary InterfaceMethodsParameterEvents Generated by Component Listener componentMoved componentHidden componentResized ComponentEvent getComponent Component Container Listener componentAdded componentRemoved ContainerEvent getChild getContainer Container FocusListenerfocusGained focusLost focusEvent IsTemporary Component KeyListenerkeyPressed keyRealsed keyTyped KeyEvent getKeyChar getKeyCode getkeyModifiersText isActionKey Component

Basic Java : Event handling in AWT and Swing 12 Event Handling Summary InterfaceMethodsParameterEvents Generated by Mouse Listener mousePressed mouseRealesed mouseEntered mouseExited mouseClicked MouseEvent getClickCount getX getY getPoint translatePoint isPopupTrigger Component MouseMotion Listener mouseDragged mouseMoved Component Window Listener windowClosing windowOpened windowIconed windowDeiconed windowClosed windowActivated windowDeactivated WindowEvent getWindow Window

Basic Java : Event handling in AWT and Swing 13 Delegation Event Model with Another Class import java.awt.*; class MyFrame extends Frame { TextField t1; Button b1; MyFrame() { t1 = new TextField(20); b1 = new Button(“Click”); add(t1,”North”); b1.addActionListener(new ButtonHandler(this)); add(b1,”South”); }

Basic Java : Event handling in AWT and Swing 14 Delegation Event Model with Another Class class ButtonHandler implements ActionListener { MyFrame f ; ButtonHandler(MyFrame mf) { f=mf; } public void actionPerformed( ActionEvent e ) { // code for processing button press. }

Basic Java : Event handling in AWT and Swing 15 Adapter Classes Many of the listener interfaces have more than one method. Thus, if a particular interface is implemented, all the methods of that interface should also be implemented. To simplify this task, listener interfaces with more than one method come with adapter classes. Adapter classes implement all the methods of an interface. You can extend the adapter class to specify the desired reaction to some methods.

Basic Java : Event handling in AWT and Swing 16 Without Adapter Classes class MyFrame extends Frame implements WindowListener { public void windowActivated(WindowEvent e){} public void windowDeactivated(WindowEvent e){} public void windowIconified(WindowEvent e){} public void windowDeiconified(WindowEvent e){} public void windowOpened(WindowEvent e){} public void windowClosed(WindowEvent e){} public void windowClosing(WindowEvent e){ System.exit(0); }

Basic Java : Event handling in AWT and Swing 17 Without Adapter Class public static void main(String args[]) { Frame f = new MyFrame(); f.setSize(100,100); f.show(); f.addWindowListener(f); }

Basic Java : Event handling in AWT and Swing 18 Using Adapter Class import java.awt.*; import java.awt.event.*; class MyFrame extends Frame { MyFrame() { addWindowListener(new WindowHandler()); }

Basic Java : Event handling in AWT and Swing 19 Adapter Classes class WindowHandler extends WindowAdapter { { public void windowClosing(WindowEvent e) { System.exit(0); }