Event Handling In Java - Event-Handling In Java (
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ActionEvent using the ActionListener
interface: The following illustrates the usage of ActionEvent and
ActionListener interface in a Classic Java Application (Example I).
//Save the file with MyEvent.java file and compile it using javac,
//once complied errors free execute it.
Import javax.swings.*;
Import java.awt.event.*;
Public class MyEvent extends JFrame
{
JButton b1;
// Main Method
Public static void main (String arg[])
{
MyEvent event = new MyEvent();
}
//Constructor for the event derived class
Public MyEvent()
{
Super(“Window Title: Event Handling”);
b1 = new Jbutton(“Click Me”);
//place the button object on the window
getContentPane().add(“center”,b1);
//Register the listener for the button
ButtonListener listen = new ButtonListener();
b1.addActionListener(listen);
//display the window in a specific size
setVisible(true);
setSize(200,200);
}
//The Listener Class
Class ButtonListener implements ActionListener
{
//Definition for ActionPerformed() method
Public void ActionPerformed(ActionEvent evt)
{
JButton source = (JButton)evt.getSource();
Source.setText(“Button Has Been Clicked, Guru!”);
}
}
}
How does the above Application work?
• The execution begins with the main method.
• An Object
of the MyEvent class is created in the main method.
• Constructor of the
MyEvent class is invoked.
• Super () method calls the constructor of the
base class and sets the title of the window as given.
• A button object
is created and placed at the center of the window.
• A Listener Object is
created.
• The addActionListener() method registers the listener object
for the button.
• SetVisible () method displays the window.
• The
Application waits for the user to interact with it.
• When the user
clicks on the button labeled “Click Me”: The “ActionEvent” event is generated.
Then the ActionEvent object is created and delegated to the registered listener
object for processing. The Listener object contains the actionPerformed() method
which processes the ActionEvent In the actionPerformed() method, the reference
to the event source is retrieved using getSource() method. The label of the
button is changed to “Button has been clicked, Guru!” using setText()
method.
•
Tools of the Trade: Since the ButtonListener
class has been declared under MyEvent class. Therefore ButtonListener class is
an inner class.
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