ui programming in java

9/21/99 www.cs.vt.edu/wwtut/ 1

UI Programming in Java

Part 4 – AWTMarc Abrams

Virginia Tech CS Deptcourses.cs.vt.edu/wwwtut/


Scripple Application Menu bar: new, close, quit Pop-up menu:

save, load, cut, paste, color, … Menu keyboard shortcuts Anonymous classes


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.


Ex. 8-1 cont: Scribble Framepublic 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}


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


Next let’s look at some awt.event classes needed…

To add menus, we’ll need some listener classes…


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);

}

http://www.ora.com/info/java/qref11/java.awt.event.WindowAdapter.html


CLASS java.awt.event.ActionListener

Java in a Nutshell Online Quick Reference for Java 1.1


public abstract interface ActionListenerextends EventListener {

// Public Instance Methods

public abstract void actionPerformed(ActionEvent e);

}

http://www.ora.com/info/java/qref11/java.awt.event.ActionListener.html


CLASS java.awt.event.KeyEventJava in a Nutshell Online Quick Reference for Java 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();

}

http://www.ora.com/info/java/qref11/java.awt.event.KeyEvent.html


CLASS java.awt.MenuItemJava in a Nutshell Online Quick Reference for Java 1.1


public class MenuItem extends MenuComponent {


1.1 public MenuItem();

public MenuItem(String label);

1.1 public MenuItem(String label, MenuShortcut s);

}

http://www.ora.com/info/java/qref11/java.awt.MenuItem.html



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)));



// 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();}

});



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();}

});



// 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();

}

}


CLASS java.awt.AWTEventJava in a Nutshell Online Quick Reference for Java 1.1


public abstract class AWTEvent extends EventObject {


public AWTEvent(Event event);

public AWTEvent(Object source, int id);

public int getID();

public String paramString();

}

http://www.ora.com/info/java/qref11/java.awt.AWTEvent.html


CLASS java.util.VectorJava in a Nutshell Online Quick Reference for Java 1.1


public class Vector extends Object implements Cloneable, Serializable {


public Vector(int initialCapacity, int capacityIncrement);

public Vector(int initialCapacity);

public Vector();

}

http://www.ora.com/info/java/qref11/java.util.Vector.html


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)


Class Diagram for Scribble See transparency


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;

Extends Component, not Canvas, making it "lightweight."


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);



// 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.

}



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);

}


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);

}


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;

}


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);

}

}


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);

}


Scribble.clear()

/** Clear the scribble. Invoked by popup menu */

void clear() {

lines.removeAllElements(); // Throw out the saved scribble

repaint(); // and redraw everything.

}


Activity for class Find a partner and study class Scribble. Answer the following…

(Click here for javadocs, here for Scribble’s code.)

1. Why isn’t Scribble’s superclass java.awt.Frame?2. In Scribble’s constructor, why are two String arrays needed (labels and commands)

which contain the same 7 words?3. Look at the call to EnableEvents() in Scribble’s constructor.

1. What class defines EnableEvents()?2. Why doesn’t class ScribbleFrame need to enable the mouse events?

4. How many points does save write to a file? One per pixel? Or what?5. How many bytes are written to the save file per point saved?6. Estimate the biggest file created that menu save could create. Then run ScribbleFrame

and check.7. 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?

8. Who calls getPreferredSize()?


Let’s see how popup menu’s cut, copy, paste work…


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)


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


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


Instantiate DataFlavorpublic static final DataFlavor dataFlavor = new

DataFlavor(Vector.class, "ScribbleVectorOfLines");

We’ll put instances of Vector on clipboard


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);

}


Method clear() /** Cut is just like a copy, except we erase the

scribble afterwards */

public void cut() { copy(); clear(); }


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. }

…


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; } }


Method paste() Does c.getContents(), where c is

clipboard

ui programming in java

Documents

public scribbleframe

public constructors1

public scribleframe

public class keyevent

public class menuitem

import java

new scrollpane pane

new scribbleframe