UI Programming in Java

1. UI Programming in Java Part 4 – AWT Marc Abrams Virginia Tech CS Dept courses.cs.vt.edu/wwwtut/ www.cs.vt.edu/wwtut/

2. Scripple Application • Menu bar: new, close, quit • Pop-up menu:save, load, cut, paste, color, … • Menu keyboard shortcuts • Anonymous classes www.cs.vt.edu/wwtut/

3. Ex. 8-1: Scribble Frame import java.awt.*; // ScrollPane, PopupMenu, MenuShortcut, etc. import java.awt.datatransfer.*; // Clipboard, Transferable,etc. import java.awt.event.*; // New event model. import java.io.*; // Object serialization streams. import java.util.zip.*; // Data compression/decomp. streams. import java.util.Vector; // To store the scribble in. import java.util.Properties; // To store printing preferences. www.cs.vt.edu/wwtut/

4. Ex. 8-1 cont: Scribble Frame public class ScribbleFrame extends Frame { /** A very simple main() method for our program. */ public static void main(String[] args){ new ScribbleFrame(); } // Remember # of open windows so we can quit when last one is // closed protected static int num_windows = 0; public ScribleFrame() { /*constructor*/ }// other functions } www.cs.vt.edu/wwtut/

5. Ex. 8-1 cont: Scribble Frame /** Create a Frame, Menu, and ScrollPane */ public ScribbleFrame() { super("ScribbleFrame"); // Create the window. num_windows++; // Count it. ScrollPane pane = new ScrollPane(); pane.setSize(300, 300); // Specify scrollpane size. this.add(pane, "Center"); // Add it to the frame. Scribble scribble; scribble = new Scribble(this, 500, 500); pane.add(scribble); // Add it to the ScrollPane www.cs.vt.edu/wwtut/

6. Next let’s look at some awt.event classes needed… • To add menus, we’ll need some listener classes… www.cs.vt.edu/wwtut/

7. http://www.ora.com/info/java/qref11/java.awt.event.WindowAdapter.htmlhttp://www.ora.com/info/java/qref11/java.awt.event.WindowAdapter.html CLASS java.awt.event.WindowAdapter Java in a Nutshell Online Quick Reference for Java 1.1 Availability: JDK 1.1 public abstract class WindowAdapter extends Object implements WindowListener { public void windowActivated(WindowEvent e); public void windowClosed(WindowEvent e); public void windowClosing(WindowEvent e); public void windowDeactivated(WindowEvent e); public void windowDeiconified(WindowEvent e); public void windowIconified(WindowEvent e); public void windowOpened(WindowEvent e); } www.cs.vt.edu/wwtut/

8. http://www.ora.com/info/java/qref11/java.awt.event.ActionListener.htmlhttp://www.ora.com/info/java/qref11/java.awt.event.ActionListener.html CLASS java.awt.event.ActionListener Java in a Nutshell Online Quick Reference for Java 1.1 Availability: JDK 1.1 public abstract interface ActionListener extends EventListener { // Public Instance Methods public abstract void actionPerformed(ActionEvent e); } www.cs.vt.edu/wwtut/

9. http://www.ora.com/info/java/qref11/java.awt.event.KeyEvent.htmlhttp://www.ora.com/info/java/qref11/java.awt.event.KeyEvent.html CLASS java.awt.event.KeyEvent Java in a Nutshell Online Quick Reference for Java 1.1 Availability: JDK 1.1 public class KeyEvent extends InputEvent { // Public Constructors public KeyEvent(Component source, int id, long when, int modifiers, int keyCode, char keyChar); // Class Methods public static String getKeyModifiersText(int modifiers); public static String getKeyText(int keyCode); // Public Instance Methods public char getKeyChar(); public int getKeyCode(); public boolean isActionKey(); } www.cs.vt.edu/wwtut/

10. http://www.ora.com/info/java/qref11/java.awt.MenuItem.html CLASS java.awt.MenuItem Java in a Nutshell Online Quick Reference for Java 1.1 Availability: JDK 1.0 public class MenuItem extends MenuComponent { // Public Constructors 1.1 public MenuItem(); public MenuItem(String label); 1.1 public MenuItem(String label, MenuShortcut s); } www.cs.vt.edu/wwtut/

11. Ex. 8-1 cont: Scribble Frame MenuBar menubar = new MenuBar(); // Create a menubar. this.setMenuBar(menubar); // Add it to the frame. Menu file = new Menu("File"); // Create a File menu. menubar.add(file); // Add to menubar. // Create three menu items, with menu shortcuts, add to menu. MenuItem n, c, q; file.add(n = new MenuItem("New Window", new MenuShortcut(KeyEvent.VK_N))); file.add(c = new MenuItem("Close Window",new MenuShortcut(KeyEvent.VK_W))); file.addSeparator(); // Put a separator in the menu file.add(q = new MenuItem("Quit",new MenuShortcut(KeyEvent.VK_Q))); www.cs.vt.edu/wwtut/

12. Ex. 8-1 cont: Scribble Frame // Create and register action listener objects for the three menu items. n.addActionListener(new ActionListener() { // Open a new windowpublic void actionPerformed(ActionEvent e) {new ScribbleFrame();}}); c.addActionListener(new ActionListener() { // Close this window. public void actionPerformed(ActionEvent e) {close();}}); www.cs.vt.edu/wwtut/

13. Ex. 8-1 cont: Scribble Frame q.addActionListener(new ActionListener() { // Quit the program. public void actionPerformed(ActionEvent e) {System.exit(0);}}); // Another event listener, this one to handle window close requests. this.addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) {close();}}); www.cs.vt.edu/wwtut/

14. Ex. 8-1 cont: Scribble Frame // Set the window size and pop it up. this.pack(); this.show(); } /** Close a window. If this is the last open window, just quit. */ void close() { if (--num_windows == 0) System.exit(0); else this.dispose(); } } www.cs.vt.edu/wwtut/

15. http://www.ora.com/info/java/qref11/java.awt.AWTEvent.html CLASS java.awt.AWTEvent Java in a Nutshell Online Quick Reference for Java 1.1 Availability: JDK 1.1 public abstract class AWTEvent extends EventObject { // Public Constructors public AWTEvent(Event event); public AWTEvent(Object source, int id); public int getID(); public String paramString(); } www.cs.vt.edu/wwtut/

16. http://www.ora.com/info/java/qref11/java.util.Vector.html CLASS java.util.Vector Java in a Nutshell Online Quick Reference for Java 1.1 Availability: JDK 1.0 public class Vector extends Object implements Cloneable, Serializable { // Public Constructors public Vector(int initialCapacity, int capacityIncrement); public Vector(int initialCapacity); public Vector(); } www.cs.vt.edu/wwtut/

17. Let’s look at class Scribble… • Allows drawing in colors via mouse events • Implements paint() • Implements pop-up menu(print, load/save, cut/copy/paste) www.cs.vt.edu/wwtut/

18. Class Diagram for Scribble • See transparency www.cs.vt.edu/wwtut/

19. Extends Component, not Canvas, making it "lightweight." Here’s how class Scribble starts… /** * This class is a custom component that supports scribbling. It also has * a popup menu that allows the scribble color to be set and provides access * to printing, cut-and-paste, and file loading and saving facilities. */ class Scribble extends Component implements ActionListener { protected short last_x, last_y; protected Vector lines = new Vector(256,256); protected Color current_color = Color.black; protected int width, height; protected PopupMenu popup; protected Frame frame; www.cs.vt.edu/wwtut/

20. Scribble’s constructor (1 of 3) /** This constructor requires a Frame and a desired size */ public Scribble(Frame frame, int width, int height) { this.frame = frame; this.width = width; this.height = height; // We handle scribbling with low-level events, so we must // specify which events we are interested in. this.enableEvents(AWTEvent.MOUSE_EVENT_MASK); this.enableEvents(AWTEvent.MOUSE_MOTION_EVENT_MASK); www.cs.vt.edu/wwtut/

21. Scribble’s constructor (2 of 3) // Create the popup menu using a loop. Note the separation of menu // "action command" string from menu label. Good for internationalization. String[] labels = new String[] { "Clear", "Print", "Save", "Load", "Cut", "Copy", "Paste" }; String[] commands = new String[] { "clear", "print", "save", "load", "cut", "copy", "paste" }; popup = new PopupMenu(); // Create the menu for(int i = 0; i < labels.length; i++) { MenuItem mi = new MenuItem(labels[i]); mi.setActionCommand(commands[i]); mi.addActionListener(this); popup.add(mi); // Add item to the popup menu. } www.cs.vt.edu/wwtut/

22. Scribble’s constructor (3 of 3) Menu colors = new Menu("Color"); // Create a submenu. popup.add(colors); // And add it to the popup. String[] colornames = new String[] { "Black", "Red", "Green", "Blue"}; for(int i = 0; i < colornames.length; i++) { MenuItem mi = new MenuItem(colornames[i]); mi.setActionCommand(colornames[i]); mi.addActionListener(this); colors.add(mi); } // Finally, register the popup menu with the component it appears over this.add(popup); } www.cs.vt.edu/wwtut/

23. Scribble.getPreferredSize() /** Specifies how big the component would like to be. Always returns the preferred size passed to the Scribble() constructor */ public Dimension getPreferredSize() { return new Dimension(width, height); } www.cs.vt.edu/wwtut/

24. Scribble.actionPerformed() /** This is the ActionListener method invoked by the popup menu items */ public void actionPerformed(ActionEvent event) { // Get the "action command" of the event, and dispatch based on that. // This method calls a lot of the interesting methods in this class. String command = event.getActionCommand(); if (command.equals("clear")) clear(); else if (command.equals("print")) print(); else if (command.equals("save")) save(); else if (command.equals("load")) load(); else if (command.equals("cut")) cut(); else if (command.equals("copy")) copy(); else if (command.equals("paste")) paste(); else if (command.equals("Black")) current_color = Color.black; else if (command.equals("Red")) current_color = Color.red; else if (command.equals("Green")) current_color = Color.green; else if (command.equals("Blue")) current_color = Color.blue; } www.cs.vt.edu/wwtut/

25. Scribble.paint() /** Draw all the saved lines of the scribble, in the appropriate colors */ public void paint(Graphics g) { for(int i = 0; i < lines.size(); i++) { Line l = (Line)lines.elementAt(i); g.setColor(l.color); g.drawLine(l.x1, l.y1, l.x2, l.y2); } } www.cs.vt.edu/wwtut/

26. Scribble’s processMouseEvent /** * This is the low-level event-handling method called on mouse events * that do not involve mouse motion. Note the use of isPopupTrigger() * to check for the platform-dependent popup menu posting event, and of * the show() method to make the popup visible. If the menu is not posted, * then this method saves the coordinates of a mouse click or invokes * the superclass method. */ public void processMouseEvent(MouseEvent e) { if (e.isPopupTrigger()) // If popup trigger, popup.show(this, e.getX(), e.getY()); else if (e.getID() == MouseEvent.MOUSE_PRESSED) { last_x = (short)e.getX(); last_y = (short)e.getY(); } else super.processMouseEvent(e); } www.cs.vt.edu/wwtut/

27. Scribble.clear() /** Clear the scribble. Invoked by popup menu */ void clear() { lines.removeAllElements(); // Throw out the saved scribble repaint(); // and redraw everything. } www.cs.vt.edu/wwtut/

28. Activity for class • Find a partner and study class Scribble. • Answer the following… (Click here for javadocs, here for Scribble’s code.) • Why isn’t Scribble’s superclass java.awt.Frame? • In Scribble’s constructor, why are two String arrays needed (labels and commands) which contain the same 7 words? • Look at the call to EnableEvents() in Scribble’s constructor. • What class defines EnableEvents()? • Why doesn’t class ScribbleFrame need to enable the mouse events? • How many points does save write to a file? One per pixel? Or what? • How many bytes are written to the save file per point saved? • Estimate the biggest file created that menu save could create. Then run ScribbleFrame and check. • What sequence of events that occurs from the time the user clicks the right mouse button until the method associated with a popup menu item (e.g., method Scribble.print()) is called? Is processMouseEvent() called one time or two times? • Who calls getPreferredSize()? www.cs.vt.edu/wwtut/

29. Let’s see how popup menu’s cut, copy, paste work… www.cs.vt.edu/wwtut/

30. Java AWT Datatransfer • Supports underlying OS’s clipboard • Operations: copy, cut, paste • Handles one object at a time • Java 2 permits drag & drop • to/from non-Java apps • between Java apps • w/in one Java app (from jdk 1.1.x) www.cs.vt.edu/wwtut/

31. JAVA AWT DATATRANSFER • 3 classes • Clipboard (provided by OS) • DataFlavor (flavor = mime type) • user defined class to put on system Clipboard (contains cut/copied data + DataFlavor) • 2 interfaces • Clipboard Owner • Transferable • 1 exception • UnsupportedFlavorException www.cs.vt.edu/wwtut/

32. JAVA AWT DATATRANSFER • User class must implement two interfaces (ClipboardOwner and Transferable) and must • remembers an object • returns object • Clipboard Owner:notifies you when data is removed www.cs.vt.edu/wwtut/

33. Instantiate DataFlavor public static final DataFlavor dataFlavor = new DataFlavor(Vector.class, "ScribbleVectorOfLines"); • We’ll put instances of Vector on clipboard www.cs.vt.edu/wwtut/

34. Method cut() public void copy() { // Get system clipboard Clipboard c = this.getToolkit().getSystemClipboard(); // Copy and save the scribble in a Transferable object SimpleSelection s = new SimpleSelection(lines.clone(), dataFlavor); // Put that object on the clipboard c.setContents(s, s); } www.cs.vt.edu/wwtut/

35. Method clear() /** Cut is just like a copy, except we erase the scribble afterwards */ public void cut() { copy(); clear(); } www.cs.vt.edu/wwtut/

36. Class SimpleSelection (1 of 2) static class SimpleSelection implements Transferable, ClipboardOwner { protected Object selection; // The data to be transferred. protected DataFlavor flavor; // The one data flavor supported. public SimpleSelection(Object selection, DataFlavor flavor) { this.selection = selection; // Specify data. this.flavor = flavor; // Specify flavor. } … www.cs.vt.edu/wwtut/

37. Class SimpleSelection (1 of 2) public DataFlavor[] getTransferDataFlavors() { return new DataFlavor[] { flavor }; } public boolean isDataFlavorSupported(DataFlavor f) { return f.equals(flavor); } public Object getTransferData(DataFlavor f) throws UnsupportedFlavorException { if (f.equals(flavor)) return selection; else throw new UnsupportedFlavorException(f); } public void lostOwnership(Clipboard c, Transferable t) { selection = null; } } www.cs.vt.edu/wwtut/

38. Method paste() • Does c.getContents(), where c is clipboard www.cs.vt.edu/wwtut/