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WindowEvent and WindowListener





An event of type WindowEvent is generated in such situations -




Some methods of WindowEvent class


Method Description
public Window getWindow() Returns the window which triggered the WindowEvent.
public int getNewState() Returns the new state of the window.





A class to listen & respond to a WindowEvent must perform the next two steps:


Method Description
public void addWindowListener(ItemListener object) where object is an object of the class that has implemented Windowistener interface. Doing this, registers the class to listen and respond to WindowEvent.



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Handling an WindowEvent by implementing WindowListener interface


In the upcoming code, we are going to create a class that will listen to WindowEvent, by implementing WindowListener interface. In this code, WindowEvent is generated when a key is pressed and released within a textfield.

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


public class WindowEx1 implements WindowListener
{
Label label1;
Frame frame;


WindowEx1()
{

frame = new Frame("Handling KeyEvent");

label1= new Label("-See window events -", Label.CENTER);

frame.setLayout(new FlowLayout());
frame.add(label1);

//Registering class WindowEx1 to catch and respond to window events 
frame.addWindowListener(this); 

frame.setSize(340,200);
frame.setVisible(true);
}


public void windowActivated(WindowEvent we)
{
System.out.println("Window Activated");
}

public void windowClosed(WindowEvent we)
{
System.out.println("Window Closed");
}

public void windowClosing(WindowEvent we)
{
frame.dispose();
System.out.println("Window Closing");
}

public void windowDeactivated(WindowEvent we)
{
System.out.println("Window Deactivated");
}

public void windowDeiconified(WindowEvent we)
{
System.out.println("Window Deiconified");
}

public void windowIconified(WindowEvent we)
{
System.out.println("Window Iconified/minimized");
}

public void windowOpened(WindowEvent e)
{
System.out.println("Window Opened for the first time");
}

public static void main(String... ar)
{
new WindowEx1();
}

}

When you run the code, you are presented a window shown in the window below -:

Figure 1


At the command prompt you are displayed two messages, due to the execution of methods in sequence:
Window Activated
Window Opened for the first time



When you click on the minimize button of this window to minimize it, the window is deactivated and deiconified.
Figure 2


Hence, two new messages are displayed on the command prompt, due to the execution of methods in sequence:
Window Iconified/minimized
Window Deactivated



When you bring up the minimized window, the window is reactivated.

Figure 3



Hence, a new message is displayed on the command prompt, due to the execution of the method:
Window Activated



When you click on the (x) button of this window to close it, the window is deactivated and closed.

Figure 4



Hence, three new messages are displayed on the command prompt, due to the execution of methods in sequence:
Window Closing
Window Deactivated
Window Closed




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