Embed Size (px)
Citation preview
1Java Lectures
User interfaces and Swing
● Overview,– applets, drawing, action listening, layout
managers.
● APIs:– java.awt.*,
– javax.swing.*, classes names start with a J.
2Java Lectures
Applets
public class Simple extends Applet {public void init() { . . . }public void start() { . . . }public void stop() { . . . }public void destroy() { . . . }
}
init() to initialize the applet each time it's loaded (or reloaded). start() to start the applet's execution, such as when the applet's loaded or when the user revisits a page that contains the applet. stop() to stop the applet's execution, such as when the user leaves the applet's page or quits the browser. destroy() to perform a final cleanup in preparation for unloading.
3Java Lectures
Run an applet
<HTML><BODY><APPLET CODE=SimpleApplet.class WIDTH=200 HEIGHT=100></APPLET></BODY></HTML>
appletviewer simpleApplet.html
file simpleApplet.html
4Java Lectures
Applets and standalone applications
● The user interface is attached to a panel object nested– for applets, in a top-level browser,
– for a swing application: in a top-level frame object.
● A frame object is a top-level window that provides a title, banner, and methods to manage the appearance and behavior of the window.
5Java Lectures
A simple window
● upper left corner, coordinates (200, 100) from the upper left corner of the screen.
● width: 300 pixels; height: 350 pixels.
the whole is an instance of javax.swing.JFrame.
container of the window
6Java Lectures
Code of the simple window
import javax.swing.JFrame;
class Window { public static void main(String[] args) {
JFrame cadre = new JFrame("Empty");cadre.setSize(300, 350);cadre.setLocation(200, 100);cadre.show();
}}
7Java Lectures
A small application
JFrame
JPanel
JPanel
JPanel
JButton
8Java Lectures
import javax.swing.*;import java.awt.event.*;import java.awt.*;
class Container extends JPanel implements ActionListener { JButton show = new JButton("show");JButton erase = new JButton("erase");JPanel board = new JPanel();
Container() {
setLayout(new BorderLayout(5, 5));
JPanel theButtons = new Jpanel(); // for the buttonstheButtons.add(show);theButtons.add(erase);add(theButtons, BorderLayout.NORTH);
board.setPreferredSize(new Dimension(200, 150));board.setBackground(Color.white);add(board, BorderLayout.CENTER);
show.addActionListener(this);erase.addActionListener(this);
}...
9Java Lectures
public void actionPerformed(ActionEvent e) {Object source = e.getSource();
if (source == show) {Graphics g = board.getGraphics();
g.setColor(Color.red);g.drawOval(50,20,100,100);g.dispose();
} else if (source == erase) {board.repaint();
}}
public static void main(String[] argv) {
JFrame myFrame = new JFrame();myFrame.setContentPane(new Container());myFrame.pack();myFrame.show(); // or myFrame.setVisible(true);
}}
10Java Lectures
Drawing
● Every JComponent object contains:
– a background and a foreground color,● public Color getForeground();
● public void setForeground(Color c);
– a font,● public Font getFont();
● public void setFont(Font f);
– a method, ● public Graphics getGraphics();
11Java Lectures
The Graphics class
● Magic pencil for a graphical component.● It holds a graphic context:
– the painted component,
– a color for drawing: setColor(Color c);
– a font: setFont(Font f);
– a "clipping" rectangle (render area),– draw methods,
● drawRect(), drawLine()...
12Java Lectures
Paint
● repaint() calls the paint() method, which calls the method paintComponent(),
– then a method to repaint the borders,
– then the paint() methods of the sub-components, down the containment hierarchy.
13Java Lectures
Button: Action listening
● The interface ActionListener contains only one method declaration– public void actionPerformed(ActionEvent e);
● How button-generated actions are passed to the actionPerformed method ?
– trace.addActionListener(delegate);
– the delegate object must implement ActionListener, and thus has a method actionPerformed.
14Java Lectures
Action listening
– means: when the button show is clicked, the method actionPerformed of delegate is invoked.
– an ActionEvent object is created when the button is clicked, and passed to actionPerformed.
– Event handling in the actionPerformed method:
● for example, drawing.
15Java Lectures
Events
● Click a button,● Chose an item in a menu,● Push the button of the mouse/move the
mouse while the pointer is on a component,● Type "return" when working in a text area,● Close the window of the application,● Press any key.● ...
16Java Lectures
Action listening and event handling
● Events are "perceived" by the computer– passed to the Java program, treating the event,
according to the type of event and the concerned component.
– ActionEvent objects are created, representing the event.
● Listeners are objects which treat some kind of events, implementing the right interface.– they are linked to a certain source (component),– they have methods to handle the events.
17Java Lectures
Other ActionListeners
● Many...● An adapter class implements empty versions
of all its interface's methods.– use inner classes.
Source
listener1
listener2
listener3
18Java Lectures
The event-dispatching thread
● It does event handling and the different painting operations on the screen,
● It treats everything sequentially: while an event is treated, the UI is suspended.
19Java Lectures
Another example: Mouse clicks
20Java Lectures
The MouseListener interface
● This listener allows to treat 5 types of events,– public void mousePressed(MouseEvent evt);
– public void mouseReleased(MouseEvent evt);
– public void mouseEntered(MouseEvent evt);
– public void mouseExited(MouseEvent evt);
– public void mouseClicked(MouseEvent evt);
21Java Lectures
A class for the circles
class GraphicCircle {int x,y, radius;
GraphicCircle(int radius, int x, int y) {this.radius = radius;this.x = x;this.y = y;
} public void draw(Graphics g) {g.fillOval(x - radius, y - radius,
2*radius, 2*radius);}
}
22Java Lectures
class TestClicks extends JPanel implements MouseListener {Vector memory = new Vector();
TestClicks() {setPreferredSize(new Dimension(250, 250));addMouseListener(this);
}
public void mouseClicked(MouseEvent evt) {memory.add(new GraphicCircle(15, evt.getX(),
evt.getY()));repaint();
}
public void mousePressed(MouseEvent evt) {}public void mouseReleased(MouseEvent evt) {}public void mouseEntered(MouseEvent evt) {}public void mouseExited(MouseEvent evt) {} ...
23Java Lectures
public void paintComponent(Graphics g) {super.paintComponent(g);for (int i = 0; i < memory.size(); i++)((GraphicCircle)memory.get(i)).draw(g);
}
public static void main(String[] args) {JFrame frame = new JFrame();frame.setContentPane(new TestClicks());frame.setLocation(50, 50);frame.pack();frame.setVisible(true);
}}
24Java Lectures
Layout managers
● java.awt.FlowLayout (default for JPanel): from left to right, starting new rows if necessary.
25Java Lectures
Layout managers (2)
● java.awt.BorderLayout (default for content pane): five areas available to hold components, north, south, east, west, and center. All extra space is placed in the center area.
● javax.swing.BoxLayout: puts components in a single row or column. It respects the components' requested maximum sizes, and also lets you align components.
26Java Lectures
Layout managers (3)
● javax.swing.CardLayout: implements an area that contains different components at different times.
● javax.swing.GridLayout: displays components in a grid.
● javax.swing.GridBagLayout: aligns components by placing them within a grid of cells, allowing some components to span more than one cell.
27Java Lectures
Some design solution
● Main advice: separate the user interface from the application. 2 classes,– the user interface,
– the application, implementing the ActionListener.
28Java Lectures
class Delegate implements MouseListener {Jpanel panel;
Delegate(JPanel _panel) {this.panel = _panel;
}
public void mouseClicked(MouseEvent evt) {panel.addCircle(new GraphicCircle(15, evt.getX(),
evt.getY()));repaint();
}
public void mousePressed(MouseEvent evt) {}public void mouseReleased(MouseEvent evt) {}public void mouseEntered(MouseEvent evt) {}public void mouseExited(MouseEvent evt) {}
}
29Java Lectures
class TestClicks extends JPanel {Vector memory = new Vector();
TestClicks() {setPreferredSize(new Dimension(250, 250));addMouseListener(new Delegate(this));
}
public void addCircle(GraphicCircle c) {memory.add(c);
}
public void paintComponent(Graphics g) {super.paintComponent(g);for (int i = 0; i < memory.size(); i++)((GraphicCircle)memory.get(i)).draw(g);
} ...
30Java Lectures
public static void main(String[] args) {JFrame frame = new JFrame();frame.setContentPane(new TestClicks());frame.setLocation(50, 50);frame.pack();frame.setVisible(true);
}}
