AWT Part-2

196. What are the problems faced by Java programmers who don’t use layout managers?
Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizing  and positioning that will work within the constraints imposed by each windowing system.



























Handling Events with an Anonymous Class
If an event handler is specific to a component (that is, not shared by other components), there is no need to declare a class to handle the event. The event handler can be implemented using an anonymous inner class. This example demonstrates an anonymous inner class to handle key events for a component.


component.addKeyListener(new KeyAdapter() {
public void keyPressed(KeyEvent evt) {

  }

});



Handling Action Events
Action events are fired by subclasses of AbstractButton and includes buttons, checkboxes, and menus.


AbstractButton button = new JButton(quot;OK”);
button.addActionListener(new MyActionListener());


public class MyActionListener
implements ActionListener {
public void actionPerformed(ActionEvent evt) {
// Determine which abstract
// button fired the event.
AbstractButton button =
(AbstractButton)evt.getSource();

   }

}

Handling Key Presses
You can get the key that was pressed either as a key character (which is a Unicode character) or as a key code (a special value representing a particular key on the keyboard).


component.addKeyListener(new MyKeyListener());


public class MyKeyListener extends KeyAdapter {
public void keyPressed(KeyEvent evt) {
// Check for key characters.
if (evt.getKeyChar() == ‘a’) {
process(evt.getKeyChar());

    }



// Check for key codes.
if (evt.getKeyCode() == KeyEvent.VK_HOME) {
process(evt.getKeyCode());

    }

  }

}

Handling Mouse Clicks
component.addMouseListener(
new MyMouseListener());


public class MyMouseListener
extends MouseAdapter {
public void mouseClicked(MouseEvent evt) {
if ((evt.getModifiers() &
InputEvent.BUTTON1_MASK) != 0) {
processLeft(evt.getPoint());

      }

if ((evt.getModifiers() &
InputEvent.BUTTON2_MASK) != 0) {
processMiddle(evt.getPoint());

      }

if ((evt.getModifiers() &
InputEvent.BUTTON3_MASK) != 0) {
processRight(evt.getPoint());

      }

    }

}

Handling Mouse Motion
component.addMouseMotionListener(
new MyMouseMotionListener());


public class MyMouseMotionListener
extends MouseMotionAdapter {
public void mouseMoved(MouseEvent evt) {
// Process current position of cursor
// while all mouse buttons are up.
process(evt.getPoint());

        }

public void mouseDragged(MouseEvent evt) {
// Process current position of cursor
// while mouse button is pressed.
process(evt.getPoint());

        }

    }

Detecting Double and Triple Clicks
component.addMouseListener(
new MyMouseListener());


public class MyMouseListener extends MouseAdapter {
public void mouseClicked(MouseEvent evt) {
if (evt.getClickCount() == 3) {
// triple-click
} else if (evt.getClickCount() == 2) {
// double-click

    }

  }

}

Handling Focus Changes
component.addFocusListener(
new MyFocusListener());


public class MyFocusListener
extends FocusAdapter {
public void focusGained(FocusEvent evt) {
// The component gained the focus.

    }

public void focusLost(FocusEvent evt) {
// The component lost the focus.

    }

}