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Events on Java

  Asked By: Meenachi    Date: Aug 20    Category: Java    Views: 631
  

Can someone tell me how to use events in Java? There's some class
or it's just a reserved word as in c#? If it's a class, which is it
and it locates in which package.

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2 Answers Found

 
Answer #1    Answered By: Chau Tran     Answered On: Aug 20

You have to import java.awt.event*
then if you have a text field for example myTextField
you have to write a kinda special code, like:

myTextField.addActionListener (
new ActionListener()
{
public void actionPerformed (ActionEvent e)

// Whatever is gonna happen here
}
);

This is the way it works, the same goes for the other
listeners, but please check the API, I might have
misspelled something.

 
Answer #2    Answered By: Viheke Fischer     Answered On: Aug 20

Common events  are residing in java.awt.event package  and javax.swing.event
package.
Basically all events are Interface types so there is only method
declaration, & allows you to inherit as many as Interface if u want.
While using these interfaces you have to override the method already
declared in parent interface and put some of your code here to do some action.
Basically java  SWING / AWT are using this Event Driven Model, simply user
has to Click / Enter something to do some action.

Some common properties for Events in Java

1. All Event Listeners are Interface & having public, void signatures,
so NO event will return something to user.
3. You can use Adapter classes if u dont want to override all the
methods of a Interface, in my example I have used WindowAdapter class  &
Overridden only windowClosing() method, simply Event Adapter will put null body
on the methods which u r not overridden
4. Interface methods have EventObject as parameter which will give
additional info about this Event, like getSource(), getX(),getY()
5. You can remove a listener to the component using
remove<ListenerName>() methods

if I am wrong on something here plz let me know


example:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ActionDemo extends JFrame implements ActionListener
{
JButton jbtnDemo = new JButton("Click Here");

public ActionDemo()
{
super("Action Listener Demo");
setSize(150,100);
Container c = getContentPane();
c.setLayout(new FlowLayout(FlowLayout.CENTER));
c.add(jbtnDemo);
validate();
pack();
show();

jbtnDemo.addActionListener(this); //this will add the listener to
this button so that if any body clicks this button the actionPerformed() method
will be fired

addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent we)
{
dispose();
System.exit(0);
}
});
}

public void actionPerformed(ActionEvent ae)
{
if(ae.getSource() == jbtnDemo)
{
JOptionPane.showMessageDialog(this,"You have clicked on me
:)","Click Here",JOptionPane.INFORMATION_MESSAGE);
}
}

public static void main(String args[])
{
new ActionDemo();
}
}

 
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