Download java.awt

Implementing GUIs in Java
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The Java Foundation Classes (JFC) are a set of
packages encompassing the following APIs:
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Abstract Window Toolkit (AWT): native GUI
components
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Swing: lightweight GUI components
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2D: rendering two-dimensional shapes, text, and
images
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Accessibility: allowing compatibility with, for
example, screen readers and screen magnifiers
Abstract Window Toolkit (AWT)
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Provides basic UI components:
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Buttons, lists, menus, textfields, etc
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Event handling mechanism
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Clipboard and data transfer
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Image manipulation
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Font manipulation
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Graphics
Platform independence is achieved through peers,
or native GUI components
AWT Packages
java.awt
java.awt.accessibility
java.awt.color
java.awt.datatransfer
java.awt.dnd
java.awt.event
java.awt.font
java.awt.geom
java.awt.im
java.awt.image
java.awt.peer
java.awt.print
java.awt.swing
Basic component functionality
Assistive technologies
Colors and color spaces
Clipboard and data transfer support
Drag and drop
Event classes and listeners
2D API font package
2D API geometry package
Input methods
Fundamental image manipulation classes
Peer interfaces for component peers
2D API support for printing
Swing components
Peers and Platform Independence
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The first AWT (Java 1.0) was rolled out in an
incredible 6 weeks using peers
Thus an AWT menu on the Solaris platform, for
example, actually creates a Motif menu object as
its peer
UI components that have peers are called
heavyweight because
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they are rendered in their own (opaque) windows and
thus are expensive to use,
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they must be rectangular and cannot have transparent
backgrounds, and
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they are not amenable to being subclassed
Using Peers
Java
Program
Java
AWT
Native
Window
System
Peers
A Java program creates and displays an AWT component,
which creates and displays a native component, or peer.
Lightweight Components
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AWT 1.1 introduced the notion of lightweight
components which:
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are contained within a heavyweight component's
window
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do not have peers
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are rendered in their container's window rather than
one of their own
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do not incur performance penalties and can have
transparent backgrounds
Almost all Swing components are lightweight
ones that extend either java.awt.Component
or java.awt.Container
Some AWT Components
Object
Component
Container
List
JComponent
Scrollbar
Label
Canvas
Button
AWT vs. Swing
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Swing does not replace the AWT; it is built on top
of it
All 1.0 AWT components are heavyweight;
corresponding Swing components are lightweight
Swing component names begin with ``J'':
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Component (AWT) vs. JComponent (Swing)
Button (AWT) vs. JButton (Swing)
Always use Swing components; however, since
Swing is built on top of AWT, you will need to
know some AWT methods
Some Swing Components
JComponent
AbstractButton
JButton
JLabel
JMenuIte
m
JToggleButton
JList
JScrollBar
JCheckBox
JFileChooser
JComponents
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Note that JComponents are containers
JComponents do not extend their AWT
counterparts:
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For example, the JButton class is not a subclass
(direct or indirect) of Button
However, some Swing components are not
JComponents
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For example, some Swing containers are direct
subclasses of their AWT counterparts
Some AWT Containers
Container
JComponent
Panel
ScrollPane
Window
Dialog
Applet
Frame
Swing Components That Are Not
JComponents (in red)
Container
JComponent
Panel
ScrollPane
Window
Dialog
Frame
Applet
JFrame
JApplet
JWindow
JDialog
Some More Swing Components That
Are JComponents
JComponent
JLayeredPane
JPanel
JScrollPane
JDesktopPane
JInternalFrame
JTable
JTree
Some AWT Component Methods
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void
void
void
void
void
void
void
setBackground(Color c)
setForeground(Color c)
setEnabled(boolean b)
setVisible(boolean b)
setFont(Font f)
setSize(Dimension d)
setLocation(int x, int y)
All but setSize and setLocation are overridden
by the JComponent class.
Example: A Simple Framed Window
import java.awt.*;
import javax.swing.*;
public class SwingTest {
public static void main(String[] args) {
JFrame frame = new JFrame("Test Frame");
frame.setSize(new Dimension(300,200));
frame.setLocation(100,100);
frame.setVisible(true);
}
}
Notes on the Example
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setSize and setLocation require
java.awt.*; the rest require javax.swing.*
The JFrame constructor argument is used as a title
The Dimension constructor takes an integer width
and height, respectively
The setLocation method takes a pair of integer
coordinates (x,y) where (0,0) is the upper left corner of
the display
The visibility of a JFrame is set to false by default
Example Output Display
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This window was managed by the K Desktop
Environment (KDE)
Clicking the Close button (X) will cause the display
to be hidden, but the program will continue since no
listeners are set up yet
Can use ctl-C to kill the Java Virtual Machine
Adding Color
The java.awt.Color class has the following static
fields (data members):
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Color.black
Color.blue
Color.cyan
Color.darkGray
Color.gray
Color.green
Color.lightGray
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Color.magenta
Color.orange
Color.pink
Color.red
Color.white
Color.yellow
Changing Background Color
import java.awt.*;
import javax.swing.*;
public class SwingTest {
public static void main(String[] args) {
JFrame frame = new JFrame("Test Frame");
frame.setSize(new Dimension(300,200));
frame.setLocation(100,100);
Container contentPane = frame.getContentPane();
contentPane.setBackground(Color.red);
frame.setVisible(true);
}
}
Content Panes
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Q: Why not just: frame.setBackground(Color.red); ?
A: In order to be lightweight, Swing's top-level
window objects must be built on top of a
lightweight AWT Container object introduced
in version 1.1
This container is called a content pane
Swing top-level window classes:
– JWindow
– JFrame
– JApplet
– JDialog
Adding a Label and Button
import java.awt.*;
import javax.swing.*;
public class SwingTest {
public static void main(String[] args) {
JFrame frame = new JFrame("Test Frame");
frame.setSize(new Dimension(300,200));
frame.setLocation(100,100);
Container contentPane = frame.getContentPane();
JLabel label = new JLabel("HERE IS A LABEL");
contentPane.add(label, BorderLayout.NORTH);
JButton button = new JButton("BUTTON");
contentPane.add(button, BorderLayout.SOUTH);
frame.setVisible(true);
}
}
New Display
Resized
Notes on the Code
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Since the frame is a top-level Swing window,
components must be added to its content pane
When components are added to a container, how
they are placed is dependent upon the container's
layout manager
The default layout manager for a JFrame is a
BorderLayout manager (described later)
When adding to a container whose layout
manager is BorderLayout, the second
parameter should be a location defined in the
BorderLayout class
Adding a List of Options
import java.awt.*;
import javax.swing.*;
public class SwingTest {
public static void main(String[] args) {
JFrame frame = new JFrame("Test Frame");
frame.setSize(new Dimension(300,200));
frame.setLocation(100,100);
Container contentPane = frame.getContentPane();
JLabel label = new JLabel("HERE IS A LABEL");
contentPane.add(label, BorderLayout.NORTH);
JButton button = new JButton("BUTTON");
contentPane.add(button, BorderLayout.SOUTH);
String[] options = {"Option 1", "Option 2",
"Option 3"};
JList list = new JList(options);
contentPane.add(list, BorderLayout.CENTER);
frame.setVisible(true);
}
}
New Display
Note that "Option 3" has been selected.
Adding a Check Box and Slider
public class SwingTest {
public static void main(String[] args) {
JFrame frame = new JFrame("Test Frame");
frame.setSize(new Dimension(400,200));
frame.setLocation(100,100);
Container contentPane = frame.getContentPane();
JLabel label = new JLabel("HERE IS A LABEL");
contentPane.add(label, BorderLayout.NORTH);
JButton button = new JButton("BUTTON");
contentPane.add(button, BorderLayout.SOUTH);
String[] options = {"Option 1", "Option 2", "Option 3"};
JList list = new JList(options);
contentPane.add(list, BorderLayout.CENTER);
JCheckBox cbox = new JCheckBox("Check");
contentPane.add(cbox, BorderLayout.WEST);
JSlider slider = new JSlider();
contentPane.add(slider, BorderLayout.EAST);
frame.setVisible(true);
}
}
New Display
Layout Management
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A layout manager determines the location and size of
components placed into a container
Different layout managers use different algorithms for
determining size and location:
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BorderLayout: places at compass locations and center
FlowLayout: places components in rows, left to right
GridLayout: places in rectangular grid
BoxLayout: places in a single row or column
Changing the Layout
public class SwingTest {
public static void main(String[] args) {
JFrame frame = new JFrame("Test Frame");
frame.setSize(new Dimension(300,200));
frame.setLocation(100,100);
Container contentPane = frame.getContentPane();
contentPane.setLayout(new FlowLayout());
JLabel label = new JLabel("HERE IS A LABEL");
JButton button = new JButton("BUTTON");
String[] options = {"Option 1", "Option 2", "Option 3"};
JList list = new JList(options);
JCheckBox cbox = new JCheckBox("Check");
JSlider slider = new JSlider();
contentPane.add(label);
contentPane.add(button);
contentPane.add(list);
contentPane.add(cbox);
contentPane.add(slider);
frame.setVisible(true);
}
}
New Display
Resized
Default Layout Managers
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The default layout manager for content panes is
BorderLayout. Recall that the following
Swing components have content panes:
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JWindow
JFrame
JDialog
JApplet
JInternalFrame
The other Swing container is the JPanel, whose
default layout manager is FlowLayout.
JPanels
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A JPanel object can be used for grouping
components into a container, which can then be
added to another container
The JPanel constructor with no arguments
creates a panel with a FlowLayout manager
Another JPanel constructor takes any layout
manager as an argument
A JPanel can also be used a a blank area for
drawing custom graphics
JPanel Example
JFrame frame = new JFrame("Test Frame");
frame.setSize(new Dimension(300,200));
frame.setLocation(100,100);
Container contentPane = frame.getContentPane();
JLabel label = new JLabel("HERE ARE SOME BUTTONS",
SwingConstants.CENTER);
JButton button1 = new JButton("BUTTON1");
JButton button2 = new JButton("BUTTON2");
JButton button3 = new JButton("BUTTON3");
JPanel panel = new JPanel();
panel.add(button1);
panel.add(button2);
panel.add(button3);
contentPane.add(label, BorderLayout.NORTH);
contentPane.add(panel, BorderLayout.CENTER);
frame.setVisible(true);
JPanel Example Output
Note use of SwingConstants.CENTER argument
in JLabel constructor.
Changing JPanel Layout
JFrame frame = new JFrame("Test Frame");
frame.setSize(new Dimension(300,200));
frame.setLocation(100,100);
Container contentPane = frame.getContentPane();
JLabel label = new JLabel("HERE ARE SOME BUTTONS",
SwingConstants.CENTER);
JButton button1 = new JButton("BUTTON1");
JButton button2 = new JButton("BUTTON2");
JButton button3 = new JButton("BUTTON3");
JPanel panel = new JPanel();
panel.setLayout
(new BoxLayout(panel, BoxLayout.Y_AXIS));
panel.add(button1);
panel.add(button2);
panel.add(button3);
contentPane.add(label, BorderLayout.NORTH);
contentPane.add(panel, BorderLayout.CENTER);
frame.setVisible(true);
New Output
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The button panel is to the west because no other
component was placed there
The BoxLayout constructor requires both the
component being laid out and either:
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BoxLayout.X_AXIS
BoxLayout.Y_AXIS
Tweaking Layouts
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Some layout constructors allow hgap and vgap,
integers specifying the number of pixels
separating components horizontally and vertically
FlowLayout allows the specification of
whether the line of components should be leftjustified, right-justified, or centered
new FlowLayout(int align)
new FlowLayout(int align, int hgap, int vgap)
new BorderLayout(int hgap, int vgap)
new GridLayout(int rows, int cols)
new GridLayout(int rows, int cols,
int hgap, int vgap)
Tweaking Example
JFrame frame = new JFrame("Test Frame");
frame.setSize(new Dimension(300,200));
frame.setLocation(100,100);
Container contentPane = frame.getContentPane();
LayoutManager lm = contentPane.getLayout();
((BorderLayout)lm).setHgap(25);
JLabel label = new JLabel("HERE ARE SOME BUTTONS",
SwingConstants.CENTER);
JButton button1 = new JButton("BUTTON1");
JButton button2 = new JButton("BUTTON2");
JButton button3 = new JButton("BUTTON3");
JPanel panel = new JPanel();
panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
panel.add(button1);
panel.add(button2);
panel.add(button3);
contentPane.add(label, BorderLayout.NORTH);
contentPane.add(panel, BorderLayout.CENTER);
frame.setVisible(true);
Tweaking Example Output
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The LayoutManager returned by
getLayout() is an interface type that the
BorderLayout class implements
The setHgap method we want is in the
BorderLayout class
So we must cast the LayoutManager to
BorderLayout in order to use setHgap
Sizing Hints
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Layout managers often need to resize their
components to make things fit
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For example, the widths and heights of components in
a BoxLayout are adjusted according to both
preferred and maximum heights and widths
If you don't like the size of the components a
layout manager comes up with, you may have to
give sizing hints using the following methods
from the JComponent class:
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void setMinimumSize(Dimension d)
void setPreferredSize(Dimension d)
void setMaximumSize(Dimension d)