Transcript Lesson_35_Review_of_the_Java__GUI

Lesson 35:
Review of the Java GUI
The JFrame, Container and
JButton
The Java Button
// helloworldbutton.java
import java.awt.*;
import javax.swing.*;
class HelloButton{
public static void main (String[] args){
JFrame frame = new JFrame("HelloButton");
Container pane = frame.getContentPane();
JButton hello = new JButton("HelloWorld");
pane.add(hello);
frame.pack();
frame.show();
}
}
frame.setSize(300,200);
The Swing library
• Any program that uses Swing to create a window enters a separate
thread of execution that enters an infinite loop, looking for events
such as mouse movements, button clicks or key presses.
• This is like having to workers executing the program:
– One for the main()
– One for watching for events
• This results in an event driven program
• When main() is finished, the program still is executing the “listening”
part of the library object.
The Swing library
• All Swing components are event sources that can be observed or
listened to.
• To use the event, we need to tell the source which object to notify when
an event occurs.
• By default the JButton reacts to a mouse click by changing its
appearance.
• JButtons are also the source of java.awt.event.ActionEvent objects. An
ActionEvent is generated by a button when you click the button with a
mouse.
• Objects that can receive events are called listeners.
• Different type of events have different listeners.
// HelloGoodBye.java
import java.awt.*;
import javax.swing.*;
Now we have a button, but no action for the
object named listener from the GoodBye
class
class HelloGoodBye{
public static void main (String[] args){
JFrame frame = new JFrame("HelloGoodBye");
Container pane = frame.getContentPane();
JButton hello = new JButton("Hello world!!");
GoodBye listener = new GoodBye();
hello.addActionListener(listener);
pane.add(hello);
frame.setSize(200,75);
frame.show();
}
}
// GoodBye.java
import java.awt.event.*;
class GoodBye implements ActionListener{
public void actionPerformed(ActionEvent e) {
System.out.println(“Goodbye !”);
System.exit(0);
}
}
The Result
The steps
• Create a button with new Jbutton (“some label”)
• Get the Container for the Jframe using getContentPane()
• Add the button to the content pane of the Jframe with add()
• Create an ActionEventListener class by
– Adding implements ActionEventListener to the lcass declaration and
– Defining an actionPerformed method
• Add the listener object to the list of listeners for the button by
calling button.addActionListener(listener), where the button
is the name we gave our button, and listener is an instance
of the class we created to be executed when the button was
clicked (the GoodBye class).
// ManyButtons.java
import java.awt.*;
import javax.swing.*;
Many Buttons
class ManyButtons{
public static void main (String[] args){
JFrame frame = new JFrame("myCalculator");
Container pane = frame.getContentPane();
JButton exit = new JButton("Exit");
GoodBye listener = new GoodBye();
exit.addActionListener(listener);
JButton myAddition = new JButton("2+2");
Addition listener1 = new Addition();
myAddition.addActionListener(listener1);
JButton mySubtraction = new JButton("123-12");
Subtraction listener2 = new Subtraction();
mySubtraction.addActionListener(listener2);
pane.add(exit);
pane.add(myAddition);
pane.add(mySubtraction);
frame.pack();
frame.show();
}
}
How not to engineer the application
// Addition.java
import java.awt.event.*;
class Addition implements ActionListener{
public void actionPerformed(ActionEvent e) {
System.out.println("The answer is 4");
System.exit(0);
}
}
// Subtraction.java
import java.awt.event.*;
class Subtraction implements ActionListener{
public void actionPerformed(ActionEvent e) {
System.out.println("The answer is 111");
System.exit(0);
}
}
// GoodBye.java
import java.awt.event.*;
class GoodBye implements ActionListener{
public void actionPerformed(ActionEvent e) {
System.out.println("Goodbye!");
System.exit(0);
}
}
How not to engineer
the application
The JTextField, JLabel
and gridLayout
// MiniCalc.java - demo gridlayout
import java.awt.*;
import javax.swing.*;
class MiniCalc{
public static void main (String[] args){
JFrame frame = new JFrame("MiniCalc");
Container pane = frame.getContentPane();
//Creating the major components
JTextField firstNumber= new JTextField(20);
JTextField secondNumber= new JTextField(20);
JTextField result= new JTextField(20);
JButton addButton = new JButton("Add");
JButton subButton = new JButton("Subtract");
pane.setLayout(new GridLayout(4,2));
Dividing the Container in a grid
with 4 rows and 2 columns
pane.add(new JLabel("Enter a number"));
pane.add(firstNumber);
pane.add(new JLabel("Enter a number"));
pane.add(secondNumber);
pane.add(new JLabel("Result"));
pane.add(result);
pane.add(addButton);
pane.add(subButton);
DoMath listener = new DoMath(firstNumber, secondNumber, result);
subButton.addActionListener(listener);
addButton.addActionListener(listener);
frame.pack();
frame.show();
}
}
// DoMath.java
import javax.swing.*;
import java.awt.event.*;
class DoMath implements ActionListener{
DoMath(JTextField first, JTextField second, JTextField result){
inputOne = first;
inputTwo = second;
output = result;
}
Simple if…else statement
public void actionPerformed(ActionEvent e){
double first, second;
first = Double.parseDouble(inputOne.getText().trim());
second = Double.parseDouble(inputTwo.getText().trim());
if (e.getActionCommand().equals("Add"))
output.setText(String.valueOf(first+second));
else
output.setText(String.valueOf(first-second));
}
private JTextField inputOne, inputTwo, output;
}
Running the application
The layout
manipulations
The LEFT layout
// FlowLayoutTest.java - demo flowlayout
CENTER
import java.awt.*;
import javax.swing.*;
class FlowLayoutTest{
public static void main (String[] args){
JFrame frame = new JFrame("FlowLayoutTest.LEFT");
Container pane = frame.getContentPane();
pane.setLayout(new FlowLayout(FlowLayout.LEFT));
pane.add(new JButton("Button 1"));
pane.add(new JLabel("Label 2"));
pane.add(new JButton("Button 3"));
pane.add(new JLabel("Label 4"));
pane.add(new JButton("Button 5"));
frame.pack();
frame.show();
}
}
LEFT
Adding buttons to actions
and frames
-Another example
Adding a button to StartTest
// StarTestQuit.java - add a quit button to StartTest
import java.awt.*;
import javax.swing.*;
class StarTestQuit{
public static void main (String[] args){
JFrame frame = new JFrame("StartTest");
Container pane = frame.getContentPane();
Star star = new Star();
JButton Quit = new JButton("Quit");
pane.setLayout(new FlowLayout());
Quit.addActionListener(new GoodBye());
pane.add(Quit);
pane.add(star);
frame.pack();
frame.show();
}
}
Adding an actionlistener to the
button based on the GoodBye
class (from earlier class example)
Adding the button and the star to the container
Packing the frame to smallest size
Showing the frame
Program
Compile
Run
Exit
A simple Drawing
program
Drawing in a frame
// StarTest.java - display a starburst
import java.awt.*;
import javax.swing.*;
class StarTest{
public static void main (String[] args){
JFrame frame = new JFrame("StartTest");
Container pane = frame.getContentPane();
Star star = new Star();
pane.add(star);
frame.pack();
frame.show();
}
}
// Star.java - draws a star
import javax.swing.*;
import java.awt.*;
The Star Class
class Star extends JComponent{
public void paint (Graphics g){
double x1, x2, y1, y2;
for (double angle=0; angle<Math.PI;
angle = angle + Math.PI / 16) {
x1=Math.cos(angle) * RADIUS + RADIUS;
y1=Math.sin(angle) * RADIUS + RADIUS;
x2=Math.cos(angle + Math.PI) * RADIUS + RADIUS;
y2=Math.sin(angle + Math.PI) * RADIUS + RADIUS;
g.drawLine((int)x1, (int)y1,(int)x2, (int)y2);
}
}
public Dimension getMinimumSize(){
return new Dimension(2 * RADIUS, 2 * RADIUS);
}
public Dimension getPreferredSize(){
return new Dimension(2 * RADIUS, 2 * RADIUS);
}
private static final int RADIUS = 100;
}
An interactive
Drawing program
// SimplePaint.java - drawing with a mouse
import java.awt.*;
import javax.swing.*;
class SimplePaint{
public static void main (String[] args){
JFrame frame = new JFrame("SimplePaint");
Container pane = frame.getContentPane();
DrawingCanvas canvas = new DrawingCanvas();
PaintListener listener=new PaintListener();
canvas.addMouseMotionListener(listener);
pane.add(canvas);
frame.pack();
frame.show();
}
}
// DrawingCanvas.java - a blank canvas
import javax.swing.*;
import java.awt.*;
class DrawingCanvas extends JComponent{
public Dimension getMinimumSize(){
return new Dimension(SIZE, SIZE);
}
public Dimension getPreferredSize(){
return new Dimension(SIZE, SIZE);
}
private static final int SIZE=500;
}
This class implements the
interface MouseMotionListener
// PaintListener.java
import java.awt.*;
import java.awt.event.*;
class PaintListener implements MouseMotionListener{
public void mouseDragged(MouseEvent e) {
DrawingCanvas canvas = (DrawingCanvas)e.getSource();
Graphics g = canvas.getGraphics();
g.fillOval(e.getX()-radius, e.getY() - radius, diameter, diameter);
}
public void mouseMoved(MouseEvent e){}
private int radius =3;
private int diameter = radius*2;
}
The interface MouseMotionListener requires that two
methods are implemented:
1) mouseDragged (button clicked and held down)
2) mouseMoved (no button clicked and held down)
The outcome
Some problems with our
simple drawing
program…
Everytime a window is
placed over the drawing,
the text that was
overlapped is removed
when the window
becomes active again
// PaintListener2.java - paints on a DrwaingCanvas2
// and it is associated with an offscreenImage.
import java.awt.*;
import java.awt.event.*;
class PaintListener2 implements MouseMotionListener{
public void mouseDragged(MouseEvent e) {
DrawingCanvas2 canvas = (DrawingCanvas2)e.getSource();
Graphics g = canvas.getGraphics();
g.fillOval(e.getX()-radius, e.getY() - radius, diameter, diameter);
// duplicating the drawing on the offscreenImage
Image image= canvas.getOffscreenImage();
g = image.getGraphics();
g.fillOval(e.getX()-radius, e.getY() - radius, diameter, diameter);
}
public void mouseMoved(MouseEvent e){}
protected int radius =3;
protected int diameter = radius*2;
}
// SimplePaint2.java - drawing with a mouse
import java.awt.*;
import javax.swing.*;
class SimplePaint2{
public static void main (String[] args){
JFrame frame = new JFrame("SimplePaint");
Container pane = frame.getContentPane();
DrawingCanvas2 canvas = new DrawingCanvas2();
PaintListener2 listener=new PaintListener2();
canvas.addMouseMotionListener(listener);
pane.add(canvas);
frame.pack();
frame.show();
}
}
// DrawingCanvas2.java - a blank canvas that remembers
// drawing operations using an offscreen image
import javax.swing.*;
import java.awt.*;
class DrawingCanvas2 extends JComponent{
public void paint(Graphics g){
if (offscreenImage!=null)
g.drawImage(offscreenImage,0,0,SIZE,SIZE,null);
}
public Image getOffscreenImage(){
if (offscreenImage==null)
offscreenImage=createImage(SIZE,SIZE);
return offscreenImage;
}
public Dimension getMinimumSize(){
return new Dimension(SIZE, SIZE);
}
public Dimension getPreferredSize(){
return new Dimension(SIZE, SIZE);
}
private static final int SIZE=500;
private Image offscreenImage;
}
Everytime a window is
placed over the drawing,
the offscreenimage is
called when the window
becomes active again
Next the
Java Applet