Event handling in Java(part 2)

LISTENER INTERFACE METHODS
ActionListener actionPerformed()
AdjustmentListener adjustmentValueChanged()
ComponentListener componentResized()
componentMoved()
componentShown()
componentHidden()
ContainerListener componentAdded()
componentRemoved()

ActionEvent
An ActionEvent is generated when a button is pressed, a
list item is double-clicked, or a menu item is selected

 public String getActionCommand()
Returns the command string associated with this
action.
 int getModifiers()
Returns the modifier keys held down during this action
event.
 String paramString()
Returns a parameter string identifying this action event

Four integer constants
 public static final int ALT_MASK
The alt modifier. An indicator that the alt key was held down during the event.
 public static final int SHIFT_MASK
The shift modifier. An indicator that the shift key was held down during the event.
 public static final int CTRL_MASK
The control modifier. An indicator that the control key was held down during the
event.
 public static final int META_MASK
The meta modifier. An indicator that the meta key was held down during the event.

ActionListener Interface
This interface defines the actionPerformed() method
that is invoked when an action event occurs.
Its general form is shown here:
void actionPerformed(ActionEvent ae)

 int getAdjustmentType( )
The amount of the adjustment can be obtained from the
getValue( ) method
 int getValue( )
For example, when a scroll bar is manipulated, this method returns
the value represented by that change.

AdjustmentListener Interface
This interface defines the adjustmentValueChanged( )
method that is invoked when an adjustment event occurs

public class AdjustmentListenerTest implements AdjustmentListener
{
Scrollbar sbar1 = new Scrollbar();
sbar1.addAdjustmentListener(this);
add(sbar1, "West");
Scrollbar sbar2=new Scrollbar();
add(sbar2,"East");
}
public void adjustmentValueChanged(AdjustmentEvent
AdjEvt)
{
System.out.println(AdjEvt.getValue());
}
}

ComponentEvent class
Indicates that a component moved, changed size, or
changed visibility.
This class has following constants.
 public static final int COMPONENT_MOVED
This event indicates that the component's position
changed.
 public static final int COMPONENT_RESIZED
This event indicates that the component's size changed.
 public static final int COMPONENT_SHOWN
This event indicates that the component was made visible.
 public static final int COMPONENT_HIDDEN
This event indicates that the component was become invisible.

ComponentListener interface
The listener interface for receiving component events.
 void componentResized(ComponentEvent e)
Invoked when the component's size changes.
 void componentMoved(ComponentEvent e)
Invoked when the component's position changes
 void componentShown(ComponentEvent e)
Invoked when the component has been made visible.
 void componentHidden(ComponentEvent e)
Invoked when the component has been made invisible.

import java.awt.*;
import java.awt.event;
public class ComponentEventExample1
{
public static void main(String[] args)
{
Frame frame = new Frame("ComponentEventExample");
TextArea txtArea = new TextArea();
Checkbox checkbox1 = new Checkbox("Checkbox 1");
Checkbox checkbox2 = new Checkbox("Checkbox 2");
frame.add(txtArea, BorderLayout.CENTER);
frame.add(checkbox1, BorderLayout.NORTH);
frame.add(checkbox2, BorderLayout.SOUTH);
frame.setVisible(true);
ComponentListener componentListener = new MyCompList();
frame.addComponentListener(componentListener);
}
}

class MyCompList implements ComponentListener
{
public void componentShown(ComponentEvent evt)
{
System.out.println("componentShown");
}
public void componentHidden(ComponentEvent evt)
{
System.out.println("componentHidden");
}
public void componentMoved(ComponentEvent evt)
{
System.out.println("componentMoved");
}
public void componentResized(ComponentEvent evt)
{
System.out.println("componentResized");
} }

ContainerEvent class
Indicates that a container's contents changed because a component
was added or removed
This class has following constants.
 public static final int COMPONENT_ADDED
This event indicates that a component was added to the
container.
 public static final int COMPONENT_REMOVED
This event indicates that a component was removed from the
container

ContainerListener interface
The listener interface for receiving container events
• void componentAdded(ContainerEvent e)
Invoked when a component has been added to the container.
• void componentRemoved (ContainerEvent e)
Invoked when a component has been removed from the container.

Instance Methods
• getChild()
public Component getChild()
Returns the component that is being added or removed.
• getContainer()
public Container getContainer()
Returns the container that fired this event.

Event handling in Java(part 2)

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