Transcript Lecture_29__Multiple_buttons_and_action_calls

Lesson 29:
Multiple buttons and action calls
More on 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
RECAP
• This results in an event driven program
• When main() is finished, the program still is executing the “listening”
part of the library object.
More on 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.
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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).
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// HelloGoodBye.java
import java.awt.*;
import javax.swing.*;
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();
}
}
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The Result
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The Files in Notepad
The Files in Command Prompt
Compiling and class files
The Result
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// ManyButtons.java
import java.awt.*;
import javax.swing.*;
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();
}
}
Many Buttons
// 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);
}
}
Many Buttons
// TextInput.java
Text input
import java.awt.*;
import javax.swing.*;
class TextInput {
public static void main (String[] args){
JFrame frame = new JFrame("textInput");
Container pane = frame.getContentPane();
JTextField input = new JTextField("enter text and press return");
Echo listner=new Echo();
input.addActionListener(listener);
pane.add(input);
frame.pack();
frame.show();
}
}
// Echo.java
import java.awt.event.*;
Text input
class Echo implements ActionListener{
public void actionPerformed(ActionEvent e) {
JTextField source =(JTextField)e.getSource();
String text = source.getText();
System.out.println("text");
System.exit(0);
}
}