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Programming in Java

Programming in Java. Graphics and Graphical User Interfaces. Display of AkmMimic. Classes used in Mimic. Display Components. Basic code to display components import java.applet.Applet; import java.awt.*; public class AkmMimic extends Applet { public void init () {

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Programming in Java

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  1. Programming in Java Graphics and Graphical User Interfaces Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  2. Display of AkmMimic Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  3. Classes used in Mimic Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  4. Display Components • Basic code to display components • import java.applet.Applet; • import java.awt.*; • public class AkmMimic extends Applet { • public void init () { • this.add (new TextField(20)); • this.add (new Label ("No news is good news")); • this.add (new Button ("OK")); • } • } • Applet is a type of Container • Can add components to containers • Container takes care of "laying out the components" • Default behavior for Applets is "Flow Layout" • Left to right, goes to new rows as necessary Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  5. Events • Events can occur on Components • There are many types of events • Action, Mouse, Key, Focus, Paint, Window • Listeners watch for events on component • Listeners in Java are interfaces • (must be implemented by a class) • Examples: • ActionListener, MouseListener, MouseMotionListener • Listeners are passed Event objects • Event objects contain information (e.g. x,y position of mouse) • Examples • ActionEvent, MouseEvent, KeyEvent Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  6. Events • Different components can generate different events • Button, List, TextField, MenuItem • generate ActionEvents • Any component can generate MouseEvents • To handle events, have to add listeners • Button b = new Button ("OK"); • ActionListener al = … create an action listener … • b.addActionListener (al); • ActionListener is an interface • Need a class that implements the interface • public abstract interface ActionListener • extends EventListener { • public abstract void actionPerformed (ActionEvent e); • } Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  7. Listening to the OK button • import java.applet.Applet; • import java.awt.*; • import java.awt.event.*; • public class AkmMimic extends Applet { • public void init () { • this.add (new TextField(20)); • this.add (new Label ("No news is good news")); • Button b = new Button ("OK"); • ActionListener al = new OK_Handler(); • b.addActionListener (al); • this.add (b); • } • } • class OK_Handler implements ActionListener { • public void actionPerformed (ActionEvent e) { • System.out.println ("You pressed OK"); • } • } Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  8. Applets can also Listen • import java.applet.Applet; • import java.awt.*; • import java.awt.event.*; • public class AkmMimic extends Applet • implements ActionListener { • public void init () { • this.add (new TextField(20)); • this.add (new Label ("No news is good news")); • Button b = new Button ("OK"); • b.addActionListener (this); • this.add (b); • } • public void actionPerformed (ActionEvent e) { • System.out.println ("You pressed OK"); • } • } Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  9. Copying from TextField to Label • import java.applet.Applet; • import java.awt.*; • import java.awt.event.*; • public class AkmMimic extends Applet • implements ActionListener { • TextField textfield = new TextField(20); • Label label = new Label ("No news is good news"); • public void init () { • this.add (textfield); • this.add (label)); • Button b = new Button ("OK"); • b.addActionListener (this); • this.add (b); • } • public void actionPerformed (ActionEvent e) { • label.setText (textfield.getText()); • } • } Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  10. Listeners • Some listeners have multiple methods • public abstract interface MouseListener • extends EventListener { • public abstract void mouseClicked(MouseEvent e); • public abstract void mouseEntered(MouseEvent e); • public abstract void mouseExited(MouseEvent e); • public abstract void mousePressed(MouseEvent e); • public abstract void mouseReleased(MouseEvent e); • }; • Classes that implement interfaces • MUST define code for all methods of the interface • If you only need code in one method, solution isn't clean Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  11. Handling Mouse Events • import java.applet.Applet; • import java.awt.*; • import java.awt.event.*; • public class AkmMimic extends Applet { • public void init () { • this.add (new TextField(20)); • this.add (new Label ("No news is good news")); • this.add (new Button("OK")); • this.addMouseListener (new MyMouseHandler()); • } • } • class MyMouseHandler implements MouseListener { • public void mouseClicked(MouseEvent e) { } • public void mouseEntered(MouseEvent e) { } • public void mouseExited(MouseEvent e) { } • public void mousePressed(MouseEvent e) { • System.out.println ("You pressed a mouse button"); • } • public void mouseReleased(MouseEvent e) { } • } Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  12. Using Adapters to Listen • For most listeners, there is a corresponding adapter • class MouseAdapter implements MouseListener { • public void mouseClicked(MouseEvent e) { } • public void mouseEntered(MouseEvent e) { } • public void mouseExited(MouseEvent e) { } • public void mousePressed(MouseEvent e) { } • public void mouseReleased(MouseEvent e) { } • } • You can reuse these, and only implement necessary methods • class MyMouseHandler extends MouseAdapter { • public void mousePressed (MouseEvent e) { • System.out.println ("You pressed a mouse button"); • } • } Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  13. Using MouseAdapter • mport java.applet.Applet; • import java.awt.*; • import java.awt.event.*; • public class AkmMimic extends Applet { • public void init () { • this.add (new TextField(20)); • this.add (new Label ("No news is good news")); • this.add (new Button("OK")); • this.addMouseListener (new MyMouseHandler()); • } • } • class MyMouseHandler extends MouseAdapter { • public void mousePressed(MouseEvent e) { • System.out.println ("You pressed a mouse button"); • } • } Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  14. Too many classes • A typical GUI has many buttons, components, menu items, etc. • Need a different class for each listener • Too many classes • Confuses name space • Java's solution • Anonymous, inner classes • Class is embedded in another class • Class does not have to have a name provided by developer Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  15. Anonymous Classes • import java.applet.Applet; • import java.awt.*; • import java.awt.event.*; • public class AkmMimic extends Applet { • public void init () { • this.add (new TextField(20)); • this.add (new Label ("No news is good news")); • this.add (new Button("OK")); • this.addMouseListener (new MouseAdapter () { • public void mousePressed(MouseEvent e) { • System.out.println ("You pressed a mouse button"); • }}); • } • } Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

  16. Left, Right, or Middle Button? • import java.applet.Applet; • import java.awt.*; • import java.awt.event.*; • public class AkmMimic extends Applet { • public void init () { • this.add (new TextField(20)); • this.add (new Label ("No news is good news")); • this.add (new Button("OK")); • this.addMouseListener (new MouseAdapter () { • public void mousePressed(MouseEvent e) { • if (e.isMetaDown()) { • System.out.println ("Right mouse button pressed"); • } else if (e.isAltDown()) { • System.out.println ("Middle mouse button pressed"); • } else { • System.out.println ("Left mouse button pressed"); • } • }}); • } • } Programming in Java; Instructor:Alok Mehta Graphics and Graphical User Interfaces

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