Java Unit-V PDF

Unit-V-PART-I Event Handling Any program that uses GUI (graphical user interface) such as Java application written for windows, is event driven. Event describes the change in state of any object. For Example : Pressing a button, Entering a character in Textbox, Clicking or Dragging a mouse, etc....

Unit-V-PART-I Event Handling Any program that uses GUI (graphical user interface) such as Java application written for windows, is event driven. Event describes the change in state of any object. For Example : Pressing a button, Entering a character in Textbox, Clicking or Dragging a mouse, etc. An event can be defined as changing the state of an object or behavior by performing actions. Actions can be a button click, cursor movement, keypress through keyboard or page scrolling, etc. Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE The java.awt.event package can be used to provide various event classes. Classification of Events Foreground Events Background Events Types of Events 1. Foreground Events Foreground events are the events that require user interaction to generate, i.e., foreground events are generated due to interaction by the user on components in Graphic User Interface (GUI). Interactions are nothing but clicking on a button, scrolling the scroll bar, cursor moments, etc. 2. Background Events Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE Events that don’t require interactions of users to generate are known as background events. Examples of these events are operating system failures/interrupts, operation completion, etc. Event Handling It is a mechanism to control the events and to decide what should happen after an event occur. To handle the events, Java follows the Delegation Event model. Delegation Event model It has Sources and Listeners. Delegation Event Model Source: Events are generated from the source. There are various sources like buttons, checkboxes, list, menu-item, choice, scrollbar, text components, windows, etc., to generate events. Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE Listeners: Listeners are used for handling the events generated from the source. Each of these listeners represents interfaces that are responsible for handling events. Components of Event Handling Event handling has three main components, Events : An event is a change in state of an object. Events Source : Event source is an object that generates an event. Listeners : A listener is an object that listens to the event. A listener gets notified when an event occurs. How Events are handled? A source generates an Event and send it to one or more listeners registered with the source. Once event is received by the listener, they process the event and then return. Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE Events are supported by a number of Java packages, like java.util, java.awt and java.awt.event. Important Event Classes and Interface Example of Event Handling import java.awt.*; import java.awt.event.*; import java.applet.*; import java.applet.*; Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE import java.awt.event.*; import java.awt.*; public class Test extends Applet implements KeyListener { String msg=""; public void init() { addKeyListener(this); } public void keyPressed(KeyEvent k) { showStatus("KeyPressed"); } public void keyReleased(KeyEvent k) { showStatus("KeyRealesed"); } public void keyTyped(KeyEvent k) Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE  { msg = msg+k.getKeyChar(); repaint(); } public void paint(Graphics g) { g.drawString(msg, 20, 40); } } HTML code: o/p:- Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE  Event Listener:- Listeners : A listener is an object that listens to the event. A listener gets notified when an event occurs. ActionListener Interface The Java ActionListener is notified whenever you click on the button or menu item. It is notified against ActionEvent. The ActionListener interface is found in java.awt.event package. It has only one method: actionPerformed(). actionPerformed() method The actionPerformed() method is invoked automatically whenever you click on the registered component. 1. public abstract void actionPerformed(ActionEvent e); How to write ActionListener The common approach is to implement the ActionListener. If you implement the ActionListener class, you need to follow 3 steps: 1) Implement the ActionListener interface in the class: 1. public class ActionListenerExample Implements ActionListener Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE 2) Register the component with the Listener: 1. component.addActionListener(instanceOfListenerclass); 3) Override the actionPerformed() method: 1. public void actionPerformed(ActionEvent e) 2. { 3. //Write the code here 4. } Java ActionListener Example: On Button click 1. import java.awt.*; 2. import java.awt.event.*; 3. //1st step 4. public class ActionListenerExample implements ActionListener 5. { 6. public static void main(String[] args) 7. { 8. Frame f=new Frame("ActionListener Example"); 9. final TextField tf=new TextField(); 10. tf.setBounds(50,50, 150,20); 11. Button b=new Button("Click Here"); 12. b.setBounds(50,100,60,30); 13. //2nd step Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE  14. b.addActionListener(this); 15. f.add(b);f.add(tf); 16. f.setSize(400,400); 17. f.setLayout(null); 18. f.setVisible(true); 19. } 20. //3rd step 21. public void actionPerformed(ActionEvent e) 22. { 23. tf.setText("Welcome to Javatpoint."); 24. } 25. } MouseListener Interface The Java MouseListener is notified whenever you change the state of mouse. It is notified against MouseEvent. The MouseListener interface is found in java.awt.event package. It has five methods. Methods of MouseListener interface The signature of 5 methods found in MouseListener interface are given below: 1. public abstract void mouseClicked(MouseEvent e); 2. public abstract void mouseEntered(MouseEvent e); Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE  3. public abstract void mouseExited(MouseEvent e); 4. public abstract void mousePressed(MouseEvent e); 5. public abstract void mouseReleased(MouseEvent e); Java MouseListener Example 1. import java.awt.*; 2. import java.awt.event.*; 3. public class MouseListenerExample extends Frame implements MouseListener 4. { 5. Label l; 6. MouseListenerExample() 7. { 8. addMouseListener(this); 9. l=new Label(); 10. l.setBounds(20,50,100,20); 11. add(l); 12. setSize(300,300); 13. setLayout(null); 14. setVisible(true); 15. } 16. public void mouseClicked(MouseEvent e) 17. { 18. l.setText("Mouse Clicked"); 19. } 20. public void mouseEntered(MouseEvent e) 21. { 22. l.setText("Mouse Entered"); 23. } 24. public void mouseExited(MouseEvent e) 25. { 26. l.setText("Mouse Exited"); 27. } 28. public void mousePressed(MouseEvent e) { Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE  29. l.setText("Mouse Pressed"); 30. } 31. public void mouseReleased(MouseEvent e) 32. { 33. l.setText("Mouse Released"); 34. } 35. public static void main(String[] args) 36. { 37. new MouseListenerExample(); 38. } 39. } Output: MouseMotionListener Interface The Java MouseMotionListener is notified whenever you move or drag mouse. It is notified against MouseEvent. The MouseMotionListener interface is found in java.awt.event package. It has two methods. Methods of MouseMotionListener interface The signature of 2 methods found in MouseMotionListener interface are given below: 1. public abstract void mouseDragged(MouseEvent e); 2. public abstract void mouseMoved(MouseEvent e); Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE Java MouseMotionListener Example 1. import java.awt.*; 2. import java.awt.event.*; 3. public class MouseMotionListenerExample extends Frame implements MouseM otionListener{ 4. MouseMotionListenerExample(){ 5. addMouseMotionListener(this); 6. 7. setSize(300,300); 8. setLayout(null); 9. setVisible(true); 10. } 11. public void mouseDragged(MouseEvent e) 12. { 13. Graphics g=getGraphics(); 14. g.setColor(Color.BLUE); 15. g.fillOval(e.getX(),e.getY(),20,20); 16. } 17. public void mouseMoved(MouseEvent e) 18. { 19. } 20. 21. public static void main(String[] args) 22. { 23. new MouseMotionListenerExample(); 24. } 25. } Output: Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE ItemListener Interface The Java ItemListener is notified whenever you click on the checkbox. It is notified against ItemEvent. The ItemListener interface is found in java.awt.event package. It has only one method: itemStateChanged(). itemStateChanged() method The itemStateChanged() method is invoked automatically whenever you click or unclick on the registered checkbox component. 1. public abstract void itemStateChanged(ItemEvent e); // Java AWT Program to demonstrate // Java ItemListener import java.awt.*; import java.awt.event.*; // Driver Class Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE class CheckboxExample { public static void main(String[] args) { // Create a new frame with a title. Frame frame = new Frame("Checkbox Example"); // Create a checkbox labeled "Enable Feature." Checkbox checkbox = new Checkbox("Enable Feature"); // Create an instance of MyItemListener to handle checkbox events. MyItemListener itemListener = new MyItemListener(); // Register the itemListener with the checkbox to listen for events. checkbox.addItemListener(itemListener); // Add the checkbox to the frame. frame.add(checkbox); // Set the frame size and layout. frame.setSize(300, 200); frame.setLayout(new FlowLayout()); // Make the frame visible. frame.setVisible(true); } } class MyItemListener implements ItemListener { public void itemStateChanged(ItemEvent e) { if (e.getStateChange() == ItemEvent.SELECTED) { // Respond when the checkbox is selected (checked). System.out.println("Feature is enabled."); Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE  } else { // Respond when the checkbox is deselected (unchecked). System.out.println("Feature is disabled."); } } } KeyListener Interface The Java KeyListener is notified whenever you change the state of key. It is notified against KeyEvent. The KeyListener interface is found in java.awt.event package, and it has three methods. Interface declaration Following is the declaration for java.awt.event.KeyListener interface: public interface KeyListener extends EventListener Methods of KeyListener interface The signature of 3 methods found in KeyListener interface are given below: Sr. no. Method name Description 1. public abstract void keyPressed (KeyEvent e); It is invoked when a key has been pressed. Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE 2. public abstract void keyReleased (KeyEvent e); It is invoked when a key has been released. 3. public abstract void keyTyped (KeyEvent e); It is invoked when a key has been typed. KeyListener Example In the following example, we are implementing the methods of the KeyListener interface. KeyListenerExample.java 1. // importing awt libraries 2. import java.awt.*; 3. import java.awt.event.*; 4. public class KeyListenerExample extends Frame implements KeyListener 5. { 6. Label l; 7. TextArea area; 8. // class constructor 9. KeyListenerExample() 10. { 11. // creating the label 12. l = new Label(); 13. // setting the location of the label in frame 14. l.setBounds (20, 50, 100, 20); 15. // creating the text area 16. area = new TextArea(); 17. // setting the location of text area 18. area.setBounds (20, 80, 300, 300); 19. // adding the KeyListener to the text area 20. area.addKeyListener(this); 21. // adding the label and text area to the frame Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE  22. add(l); 23. add(area); 24. // setting the size, layout and visibility of frame 25. setSize (400, 400); 26. setLayout (null); 27. setVisible (true); 28. } 29. // overriding the keyPressed() method of KeyListener interface where we set the t ext of the label when key is pressed 30. public void keyPressed (KeyEvent e) 31. { 32. l.setText ("Key Pressed"); 33. } 34. // overriding the keyReleased() method of KeyListener interface where we set the text of the label when key is released 35. public void keyReleased (KeyEvent e) 36. { 37. l.setText ("Key Released"); 38. } 39. // overriding the keyTyped() method of KeyListener interface where we set the tex t of the label when a key is typed 40. public void keyTyped (KeyEvent e) 41. { 42. l.setText ("Key Typed"); 43. } 44. // main method 45. public static void main(String[] args) 46. { 47. new KeyListenerExample(); 48. } 49. } Output: Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE WindowListener Interface The Java WindowListener is notified whenever you change the state of window. It is notified against WindowEvent. The WindowListener interface is found in java.awt.event package. It has three methods. WindowListener interface declaration The declaration for java.awt.event.WindowListener interface is shown below: 1. public interface WindowListener extends EventListener Methods of WindowListener interface WindowExample.java 1. // importing necessary libraries of awt 2. import java.awt.*; 3. import java.awt.event.WindowEvent; 4. import java.awt.event.WindowListener; 5. 6. // class which inherits Frame class and implements WindowListener interface 7. public class WindowExample extends Frame implements WindowListener { 8. 9. // class constructor 10. WindowExample() { Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE  11. 12. // adding WindowListener to the frame 13. addWindowListener(this); 14. // setting the size, layout and visibility of frame 15. setSize (400, 400); 16. setLayout (null); 17. setVisible (true); 18. } 19. // main method 20. public static void main(String[] args) { 21. new WindowExample(); 22. } 23. 24. // overriding windowActivated() method of WindowListener interface which prints the given string when window is set to be active 25. public void windowActivated (WindowEvent arg0) { 26. System.out.println("activated"); 27. } 28. 29. // overriding windowClosed() method of WindowListener interface which prints t he given string when window is closed 30. public void windowClosed (WindowEvent arg0) { 31. System.out.println("closed"); 32. } 33. 34. // overriding windowClosing() method of WindowListener interface which prints t he given string when we attempt to close window from system menu 35. public void windowClosing (WindowEvent arg0) { 36. System.out.println("closing"); 37. dispose(); 38. } 39. 40. // overriding windowDeactivated() method of WindowListener interface which pri nts the given string when window is not active Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE  41. public void windowDeactivated (WindowEvent arg0) { 42. System.out.println("deactivated"); 43. } 44. 45. // overriding windowDeiconified() method of WindowListener interface which pri nts the given string when window is modified from minimized to normal state 46. public void windowDeiconified (WindowEvent arg0) { 47. System.out.println("deiconified"); 48. } 49. 50. // overriding windowIconified() method of WindowListener interface which prints the given string when window is modified from normal to minimized state 51. public void windowIconified(WindowEvent arg0) { 52. System.out.println("iconified"); 53. } 54. 55. // overriding windowOpened() method of WindowListener interface which prints t he given string when window is first opened 56. public void windowOpened(WindowEvent arg0) { 57. System.out.println("opened"); 58. } 59. } Output: Adapter Classes Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE Java adapter classes provide the default implementation of listener interfaces. If you inherit the adapter class, you will not be forced to provide the implementation of all the methods of listener interfaces. So it saves code. o o It assists the unrelated classes to work combinedly. o It provides ways to use classes in different ways. o It increases the transparency of classes. o It provides a way to include related patterns in the class. o It provides a pluggable kit for developing an application. o It increases the reusability of the class. ava.awt.event Adapter classes Adapter class Listener interface WindowAdapter WindowListener KeyAdapter KeyListener MouseAdapter MouseListener MouseMotionAdapter MouseMotionListener FocusAdapter FocusListener ComponentAdapter ComponentListener ContainerAdapter ContainerListener WindowAdapter Example Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE In the following example, we are implementing the WindowAdapter class of AWT and one its methods windowClosing() to close the frame window. AdapterExample.java 1. // importing the necessary libraries 2. import java.awt.*; 3. import java.awt.event.*; 4. 5. public class AdapterExample { 6. // object of Frame 7. Frame f; 8. // class constructor 9. AdapterExample() { 10. // creating a frame with the title 11. f = new Frame ("Window Adapter"); 12. // adding the WindowListener to the frame 13. // overriding the windowClosing() method 14. f.addWindowListener (new WindowAdapter() { 15. public void windowClosing (WindowEvent e) { 16. f.dispose(); 17. } Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE  18. }); 19. // setting the size, layout and 20. f.setSize (400, 400); 21. f.setLayout (null); 22. f.setVisible (true); 23. } 24. 25. // main method 26. public static void main(String[] args) { 27. new AdapterExample(); 28. } 29. } Output: Unit-V-Java Notes Prepared by K.TRIVENI,Asst.Prof,CSE