Transcript Java GUIs and Graphics

Java GUIs and Graphics
CNS 3250
Outline
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Introduction
Events
Components
Layout managers
Drawing
GUIs and graphics in Java
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Portable!
Listeners and events
Components
Layout managers
A design consideration
 Data components should exist
independently from GUI components
 They should have no knowledge of GUI
 GUI components call upon data objects for
information
Why is this a good approach to use?
History
 AWT / Event Model (JDK 1.1)
 Heavyweight components
 Use OS “peers”
 Event Dispatch Thread
 Listeners to handle events
 Swing (Java 2)
 Lightweight components
 Painted via graphics (not OS peers)
 Preserves look and feel across platforms
Events
How does your program know if the user
clicks something with the mouse?
Register a listener object. When the user
clicks with the mouse, the system passes
an event object to the listener.
Listeners
Implements one of the listener interfaces:
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ActionListener
MouseListener
MouseMotionListener
WindowListener
 etc.
Listener interfaces are defined in java.awt.event
ActionListener interface
 Used with buttons, menu items, text fields
 Only one method, actionPerformed
 Takes an ActionEvent object as parameter
 ActionEvent has a method that tells the
command that triggered the name of the
event.
 For a button, the text of the button will be the
command by default.
import java.awt.event.*;
import javax.swing.*;
Red Alert!
class RedAlert extends JFrame implements ActionListener {
private JButton redAlertButton;
public RedAlert() {
redAlertButton = new JButton("Red Alert");
add(redAlertButton);
redAlertButton.addActionListener(this);
}
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals("Red Alert")) {
System.out.println("Shields up!");
}
}
public static void main(String[] args) {
RedAlert frame = new RedAlert();
frame.setSize(200, 100);
frame.setVisible(true);
}
}
import java.awt.event.*;
import javax.swing.*;
Red Alert!
class RedAlert extends JFrame implements ActionListener {
private JButton redAlertButton;
public RedAlert() {
redAlertButton = new JButton("Red Alert");
add(redAlertButton);
redAlertButton.addActionListener(this);
}
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals("Red Alert")) {
System.out.println("Shields up!");
}
}
public static void main(String[] args) {
RedAlert frame = new RedAlert();
frame.setSize(200, 100);
frame.setVisible(true);
}
}
MouseListener
Includes several
methods:
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mouseClicked
mouseEntered
mouseExited
mousePressed
mouseReleased
 Each method gets a
MouseEvent object
that tells the
coordinates of the
mouse and other info.
 All methods have to be
defined, whether you
use them or not...
MouseAdapter
 Defines all required methods for the
MouseListener interface
 Methods are empty.
 Override the methods you actually want to
use.
 Use by making your class extend
MouseAdapter.
Adapters
 All methods for the corresponding listener
interface are defined.
 Only useful if your class doesn't need to
inherit from any other class.
 Commonly used for mouse listeners, mouse
motion listeners, window listeners.
 There is no adapter for action listeners.
Why not?
Using listeners and events
 Decide what kind of listener you need
 This is usually based on the kind of input and
the type of component you will be using
 Define a class for that kind of listener
Make a class that implements the interface
or
Make a class that extends an adapter
 Register the listener with the component
 add____Listener, e.g. addActionListener
import java.awt.event.*;
import javax.swing.*;
Red Alert!
class RedAlert extends JFrame implements ActionListener {
private JButton redAlertButton;
public RedAlert() {
redAlertButton = new JButton("Red Alert");
add(redAlertButton);
redAlertButton.addActionListener(this);
}
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals("Red Alert")) {
System.out.println("Shields up!");
}
}
public static void main(String[] args) {
RedAlert frame = new RedAlert();
frame.setSize(200, 100);
frame.setVisible(true);
}
}
PolyDraw demo
Elf -- Java Ldraw display
Uses OpenGL (JOGL)
POV-Ray -- Ray tracing
Components
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Top-level containers
General-purpose containers
Displays
Controls
Text components
http://java.sun.com/docs/books/tutorial/uiswing/components/components_pics.html
Top-level containers
 Every Java GUI program must have a toplevel container.
 Frame (AWT--java.awt)
 JFrame (Swing--javax.swing)
http://java.sun.com/docs/books/tutorial/uiswing/components/components_pics.html
General-purpose containers
 Panel
(AWT)
 JPanel
(Swing)
http://java.sun.com/docs/books/tutorial/uiswing/components/components_pics.html
JPanel -- very commonly
used
Container for components
Drawing
Displays
JLabel
 Can include an image in addition to (or instead of
text)
 Can use HTML formatting
Controls
 JButton
 JComboBox
 JList
 JMenuItem
What listeners and events?
Controls
 JButton
ActionEvent
 JComboBox
ActionEvent
PopupMenuEvent
 JList
ListSelectionEvent
 JMenuItem
ActionEvent
What listeners and events?
Text components
http://java.sun.com/docs/books/tutorial/uiswing/components/text.html
JTextArea
 Used for multi-line text display and editing
 Does not handle scrolling internally (as
TextArea does)
 Add to JScrollPane to get scrolling
 Implements Scrollable interface
 Can specify whether or not editing is
allowed
 Can specify line wrapping or not
JEditorPane
 Can display HTML
 Not a "speed demon" according to our text
book
 Can get very complicated
'<html><body bgcolor="GRAY">
<center>
<img src="$BASE$MapPics/castle1.png">
<h3>Castle</h3>
</center>
A castle stands on a hill here.
It doesn\'t appear to be inhabited, but it\'s hard to say for sure.
<br></body></html>'
PolyDraw components
JFrame
JButton
JMenuBar
JMenu
JMenuItem
JLabel
JPanel
JTextField
JPanel
JScrollPane
JComboBox
Layout managers
Where should components go?
Usually: x, y coordinates.
In Java location, size, and shape of
components depends on another question:
How big will the user's display be?
 Could be anything from a huge, high-res
display to a cell phone
 Can change
Good news, bad news
Good news
 Adjusts components to fit size/shape of
container
 Can write Java GUIs with no special tools
 Works well for different fonts, languages
Bad news
 Can be difficult to get what you want
 Unexpected results
Types of layout managers
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BorderLayout
BoxLayout
CardLayout
FlowLayout
GridBagLayout
GridLayout
SpringLayout
Pictures on the following
slides are from the Java
Tutorial:
http://java.sun.com/docs/books/tutorial/uiswing/layout/visual.html
Using a layout manager
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Create (or get access to) container
Set layout manager for container
Create component
Add component to container
Container cp = getContentPane();
cp.setLayout(new BorderLayout());
JButton button = new JButton("Button 1");
cp.add(button, BorderLayout.CENTER);
These steps vary somewhat depending on the layout manager.
BorderLayout
 Very commonly used
 The center area grows/shrinks the most
 Regions are (or used to be):
Center, North, South, East, West
BoxLayout
 Relatively new
 Fillers:
 strut--1D fixed amount of space
 rigid area--2D fixed amount of space
 glue--variable amount of space, separates
components as much as possible
(Textbook says "spring" would be a better term
than "glue".)
CardLayout
 Used to switch back and forth between
different layouts in the same space
 Usually need to keep a reference to the
layout manager object so that you can
control which card is showing.
FlowLayout
 The simplest layout manager
 Can specify horizontal alignment
GridBagLayout
 Very flexible, but very complicated
 See the p. 433 in Core Java Vol. I for a
"Recipe for Making a Grid Bag Layout"
 Note Step 7: "compile, run, and enjoy"
 Must create GridBagConstraints objects
 Book recommends a helper class GBC
 NetBeans and other IDEs offer visual tools
GridLayout
 Useful for a number of components that are
the same size
 Position is determined by order that
components are added to the container
SpringLayout
 Meant to be as flexible as GridBagLayout
but "more intuitive"
It might be as flexible, but I think it's safe to
say that it isn't more intuitive.