Transcript GUI Components

Basics of GUI Programming
Chapter 11 and Chapter
22
GUI Components
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GUIs are built from GUI components.
GUI component is an object with which the
user interacts via--–
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Mouse
Keyboard
Voice
Etc;
Simple GUI Input/Output
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Java’s JOptionPane in javax.swing
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showMessageDialog static method
showInputDialog static method
Used for very simple input and output
GUI Components
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Two sets of GUI components in Java
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Swing (in package javax.swing)
AWT ( in package java.awt)
AWT
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components are automatically mapped to the platformspecific components
Tied to the local platform
Prone to platform-specific bugs
Referred to as heavyweight components
Eventually fade away
GUI Components
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Swing
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More robust, versatile, and flexible than AWT
components
Less dependent on the target platform
Referred to as lightweight components
Classification of GUI classes
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Container classes
Component classes
Helper classes
Container Classes
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Component classes that are used as containers to
contain other GUI components
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JFrame
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JPanel
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Window not contained inside another window
Container that holds other Swing components
JFrame object is a window – has a border, sizing buttons
Invisible container that holds user-interface components
Can be used as a canvas to draw graphics
Can be nested
JApplet
Java GUI API
Object
Component
Font
Color
Graphics
Container
Window
Frame
JFrame
JComponent
Panel
Applet
JApplet
JPanel
GUI Component Classes
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JButton
JTextField
JTextArea
JComboBox
JList
JRadioButton
JMenu
GUI Helper Classes
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Used by components and containers to draw
and place objects
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Graphics
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Color
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Abstract class for drawing strings, lines and simple
shapes
Specifies colors of GUI components
Font
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Specifies fonts for the text and drawings on GUI
components
GUI Helper Classes
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LayoutManager
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Interface that specifies how components are
arranged in a container
Layout Managers
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Java GUI components are placed in
containers, where they are arranged by the
container’s layout manager.
Layout manager places components in the
correct locations in the containers
Layout Managers - Examples
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FlowLayout – simplest layout manager
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Components are arranged in the container from
left to right, top to bottom in the order in which
they were added
Default manager
BorderLayout
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Has 5 regions NORTH (top), SOUTH (bottom),
EAST (right side), WEST (left side) and CENTER
JFrame methods
To create a user interface, you need to create
either a frame or an applet to hold userinterface components.
 JFrame() – constructs an untitled JFrame
object
 JFrame(String ) – constructs a JFrame object
with the specified title
JFrame methods
void setDefaultCloseOperation (int operation)
Operation tells the program what to do when the
frame is closed. Possible values are:
 DO_NOTHING_ON_CLOSE
 HIDE_ON_CLOSE
 DISPOSE_ON_CLOSE
 EXIT_ON_CLOSE
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JFrame methods
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setSize (int width, int height)
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Specified in pixels
Defined in Component class
setTitle (String title)
dispose() – eliminates calling frame and all
subcomponents
setVisible (boolean value)
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Defined in Component class
JFrame Concepts
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JFrame will display only when setVisible is
set to true
If setSize() is not used, frame will be 0x0;
nothing will be seen but the title bar.
If setDefaultCloseOperation is not used, the
program does not terminate and user must
break at the DOS prompt (windows)
JFrame Example
import javax.swing.JFrame;
public class MyFrame
{
public static void main (String args[]) {
JFrame frame = new JFrame (“My Frame”);
frame.setSize (400,300);
frame.setVisible (true);
frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
}
}
MyFrame output
JFrame Concepts
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JFrame object can have components added
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Components must be added to the content pane of the
JFrame
Think of a content pane as the “inside” of the JFrame
In Java , you can add components directly to the frame and
it automatically adds them to the content pane.
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Example: add(component);
Older versions: getContentPane().add (component);
Adding Components - JLabel
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JLabel – uneditable text
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Constructors
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public JLabel()
public JLabel (String text)
public JLabel (Icon icon)
public JLabel (String text, Icon icon, int horizontalAlignment)
setIcon(Icon b)
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Image b = new ImageIcon (“cat.gif”);
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Label1.setIcon(b);
Adding Components - JLabel
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.setHorizontalPosition
(SwingConstants.CENTER);
.setVerticalTextPosition
(SwingConstants.BOTTOM);
.setToolTipText(“This is a label”);
JTextField
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Enables user to enter data from the keyboard
Also can be used to display editable or uneditable text
Example
Design the GUI for a “guessing” game. User
should be asked to guess a number between
1 and 10. Points are deducted each time the
user guesses the wrong number.
Java application for GuessGame
import javax.swing.JFrame;
public class TestGuessGame {
public static void main (String args[])
{
GuessGame aGame = new GuessGame();
aGame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
aGame.setSize (200,200);
aGame.setVisible (true);
}
}
Output (using FlowLayout)
The GuessGame file
GuessGame.java
End (Part 1)
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JFrame
FlowLayout
BorderLayout