Transcript GUI Programming

GUI Chapter 10
Graphics context and objects
Creating a window based application
JFrame, JTextField, JButton
Containers and Controls
Graphics commands
Layout Managers
Event Handlers
Terms
GIU
component
container
coordinates
graphics context
Types of interfaces
Console applications

Using print and Scanner
A simple GUI

Using JoptionPane
A complete GUI using a Frame


Can be created using AWT
Can be create using Swing
The swing versus the AWT
AWT part of JDK v1


Mapped to platform specific components
Heavyweight
Swing introduced in V2


Platform independent components
Lightweight
Components
JButton tnOK = new JButton(“OK”);
JLabel tnOK = new JLabel(“OK”);
JTextField tfNAME = new
JTextField(“Enter Name”);
JCheckBox cbOK = new
JTextBox(“OK”);
JComboBox cmb = new
JComboBox(new String[]
{“Red”,”Green”,Blue”});
The Class chart
JComponent

AbstractButton
 Jbutton
 JToggleButton

JCheckBox
JTextComponent

JTextField
JLabel
JPanel
… many others …
Classes
Container Classes
JFrame
JDialog
JApplet
JPanel
Helper Classes


Graphics, Color, Font, FontMetrics
LayoutManager
Frames
Public class myframe {
public static void main(String[] args) {
JFrame yframe = new JFrame(“MyFrame”);
myframe.setsize(300,300);
myframe.setvisible=true;
myframe.setdefaultcloseoperation(Jframe.EXIT_ON_C
LOSE);
}
}
Frames with components
(limited example)
Import javax.swing.*;
Public class myframe {
public static void main(String[] args) {
JFrame yframe = new JFrame(“MyFrame”);
java.awt.Container mycnt = frame.getContentPane();
Jbutton btOK = new JButton(“OK”);
mycnt.add(btOK);
}
}
myframe.setsize(300,300);
myframe.setvisible=true;
myframe.setdefaultcloseoperation(Jframe.EXIT_ON_CLOSE);
Getting the screen size
Dimension ScrS =
Toolkit.getDefaultToolkit().getScreenSize();
int wid = screensize.width;
int hgt = screensize.height;
This can be used to center or dynamically size
frame.
Frame.setlocation(x,y);
Frame.setwidth(wid);
Frame.sethight(hgt);
Layout Managers
Use to determine how components will
be positioned on the frame or panel.
To create and apply a layout manager
to a component.
LayoutManager Lm = new
FlowLayout();
Frame.setLayout(LM);
Type of layout managers
Flow
Grid
Border
Others ….
Properties
.setHGap(10);
.setVGap(10);
.setAlignment(FlowLayout.RIGHT);
Creating a subclass of Frame
Import javax.swing.*;
Import java.awt.*;
Public class theframe extends Jframe {
Public theframe() {
Container mycnt = getContentPane();
mtcnt.setLayout(new FlowLayout());
Jbutton btOK = new JButton(“OK”);
mycnt.add(btOK);
}
public static void main(String[] args) {
theframe myframe = new theframe();
}
}
myframe.settitle(“Frame subclass”);
myframe.setsize(300,300);
myframe.setvisible=true;
myframe.setdefaultcloseoperation(Jframe.EXIT_ON_CLOSE);
The color Class
Color c = new Color(100,100,100)
The color constructor expects:
Color(R,G,B)
Red, Green, Blue 0-255
btnOK.setForeground( c );
The Font class
Font ( name, Style, size)
Font F = new Font(“Serif”, Font.BOLD +
Font.ITALIC, 12);
btnOK.setFont(F);
Drawing shapes
drawline
drawrect
fillrect
drawarc
fillarc
drawstring
draw3drect
drawroundedrect
drawpolygon
Making a window based
application
import javax.awt.*;
import javax.swing.*;
public class MyWindow extends JFrame {
public MyWindow() {
super(“My Window”);
setSize(400,200);
setVisible(true);
}
public void paint(Graphics g) {
super.paint(g);
g.setColor(Color.red);
g.fillRect(20,20,100,100);
}
public static void main( String args[]) {
MyWindow app1=new MyWindow();
app1.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);
}
}
Event Handlers
Event-driven programming
A change in the state of a GUI component
triggers a call to an event handler method
Event source is the object that the user
interacts with to trigger the event.
Event handler is an object with an event
handler method designed to handle a specific
event type.
Implementing Event Handlers
1 – Code a class for the event handler. The
class must implement the correct listener.

This can be the same class file as out application
runs in.
2 – Create an event handler object from the
class.
3 – Register the handler object with the GUI
component.
Event Handlers – Step 1
Create a class to implement the Handler
public class MyProgram extends JFrame implements ActionListener
{
…
/** This method will be invoked when a button is clicked */
public void actionPerformed(ActionEvent e) {
System.out.println("The " + e.getActionCommand() + " button
is " + "clicked at\n " + new java.util.Date(e.getWhen()));
}
…
}
Event Handlers – Step 2
Create event handler object
//ButtonListener btListener = new
ButtonListener();
This step may be skipped if we are
using the Program class as the event
object.
Event Handlers – Step 3
Register the event handler object with
the source object. In this example a
button.
…
private JButton jbtOk = new
JButton("OK");
jbtOk.addActionListener(this);
…
Example
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class TestActionEvent extends
JFrame implements ActionListener {
// Create two buttons
private JButton jbtOk = new
JButton("OK");
private JButton jbtCancel = new
JButton("Cancel");
public TestActionEvent() {
// Set the window title
setTitle("TestActionEvent");
// Set FlowLayout manager to arrange the
components inside the frame
getContentPane().setLayout(new
FlowLayout());
// Add buttons to the frame
getContentPane().add(jbtOk);
getContentPane().add(jbtCancel);
// Create a listener object
//ButtonListener btListener = new ButtonListener();
// Register listeners
jbtOk.addActionListener(this);
jbtCancel.addActionListener(this);
}
/** Main method */
public static void main(String[] args) {
TestActionEvent frame = new TestActionEvent();
}
frame.setDefaultCloseOperation(JFrame.E
XIT_ON_CLOSE);
frame.setSize(100, 80);
frame.setVisible(true);
/** This method will be invoked when a button is
clicked */
public void actionPerformed(ActionEvent e) {
System.out.println("The " +
e.getActionCommand() + " button is "
+ "clicked at\n " + new
java.util.Date(e.getWhen()));
}
}
Getting and Setting the value of a
TextField
Getting a value from a Textfield


String s;
s= TheTextField.getText();
Setting the value in a TextField

TheTextField.setText(“A value”);
Summary
AWT and Swing API
Containers – JFrame
Labels, TextFields and Buttons
Layout Managers
Graphics commands
Handling Events
Layout Managers