Md11 gui event handling
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Events allow Java GUI components to notify code of user interactions. Components generate events and event handlers register to receive them. When an event occurs, it is passed to all registered handlers. Event handlers decipher the event and process the user's interaction. Adapter classes provide default implementations of event handling methods so handlers only need to override needed methods, simplifying event handling code.
![Delegation Model import java.awt.*; public class TestButton { private Frame f; private Button b; public TestButton() { f = new Frame("Test"); b = new Button("Press Me!"); b.setActionCommand("ButtonPressed"); } public void launchFrame() { b.addActionListener(new ButtonHandler()); f.add(b,BorderLayout.CENTER); f.pack(); f.setVisible(true); } public static void main(String args[]) { TestButton guiApp = new TestButton(); guiApp.launchFrame(); } }](https://image.slidesharecdn.com/md11guieventhandling-111206071035-phpapp02/85/Md11-gui-event-handling-5-320.jpg)
Md11 gui event handling
- 2. Objectives Define events and event handling Write code to handle events that occur in a GUI Event Categories Java GUI Behavior Describe the concept of adapter classes, including how and when to use them
- 3. What Is an Event? Events – Objects that describe what happened Event sources – The generator of an event Event handlers – A method that receives an event object, deciphers it, and processes the user’s interaction
- 4. Delegation Model An event can be sent to many event handlers Event handlers register with components when they are interested in events generated by that component
- 5. Delegation Model import java.awt.*; public class TestButton { private Frame f; private Button b; public TestButton() { f = new Frame("Test"); b = new Button("Press Me!"); b.setActionCommand("ButtonPressed"); } public void launchFrame() { b.addActionListener(new ButtonHandler()); f.add(b,BorderLayout.CENTER); f.pack(); f.setVisible(true); } public static void main(String args[]) { TestButton guiApp = new TestButton(); guiApp.launchFrame(); } }
- 6. import java.awt.event.*; public class ButtonHandler implements ActionListener { public void actionPerformed(ActionEvent e){ System.out.println("Action occurred"); System.out.println("Button’s command is: " + e.getActionCommand()) } }
- 10. Event Adapters The listener classes that you define can extend adapter classes and override only the methods that you need Example: import java.awt.*; import java.awt.event.*; public class MouseClickHandler extends MouseAdapter { // We just need the mouseClick handler, so we use // the an adapter to avoid having to write all the // event handler methods public void mouseClicked(MouseEvent e) // Do stuff with the mouse click... } }