Java 中文官方教程 2022 版（二十五）（2）

*//where initialization occurs*
checkbox.addItemListener(this);
...
public void itemStateChanged(ItemEvent e) {
    if (e.getStateChange() == ItemEvent.SELECTED) {
        label.setVisible(true);
        ...
    } else {
        label.setVisible(false);
    }
}

component.setFocusTraversalKeysEnabled(false)

public class KeyEventDemo ...  implements KeyListener ... {
    *...//where initialization occurs:*
        typingArea = new JTextField(20);
        typingArea.addKeyListener(this);
        //Uncomment this if you wish to turn off focus
        //traversal.  The focus subsystem consumes
        //focus traversal keys, such as Tab and Shift Tab.
        //If you uncomment the following line of code, this
        //disables focus traversal and the Tab events 
        //become available to the key event listener.
        //typingArea.setFocusTraversalKeysEnabled(false);
    ...
    /** Handle the key typed event from the text field. */
    public void keyTyped(KeyEvent e) {
        displayInfo(e, "KEY TYPED: ");
    }
    /** Handle the key-pressed event from the text field. */
    public void keyPressed(KeyEvent e) {
        displayInfo(e, "KEY PRESSED: ");
    }
    /** Handle the key-released event from the text field. */
    public void keyReleased(KeyEvent e) {
        displayInfo(e, "KEY RELEASED: ");
    }
    ...
    private void displayInfo(KeyEvent e, String keyStatus){
        //You should only rely on the key char if the event
        //is a key typed event.
        int id = e.getID();
        String keyString;
        if (id == KeyEvent.KEY_TYPED) {
            char c = e.getKeyChar();
            keyString = "key character = '" + c + "'";
        } else {
            int keyCode = e.getKeyCode();
            keyString = "key code = " + keyCode
                    + " ("
                    + KeyEvent.getKeyText(keyCode)
                    + ")";
        }
        int modifiersEx = e.getModifiersEx();
        String modString = "extended modifiers = " + modifiersEx;
        String tmpString = KeyEvent.getModifiersExText(modifiersEx);
        if (tmpString.length() > 0) {
            modString += " (" + tmpString + ")";
        } else {
            modString += " (no extended modifiers)";
        }
        String actionString = "action key? ";
        if (e.isActionKey()) {
            actionString += "YES";
        } else {
            actionString += "NO";
        }
        String locationString = "key location: ";
        int location = e.getKeyLocation();
        if (location == KeyEvent.KEY_LOCATION_STANDARD) {
            locationString += "standard";
        } else if (location == KeyEvent.KEY_LOCATION_LEFT) {
            locationString += "left";
        } else if (location == KeyEvent.KEY_LOCATION_RIGHT) {
            locationString += "right";
        } else if (location == KeyEvent.KEY_LOCATION_NUMPAD) {
            locationString += "numpad";
        } else { // (location == KeyEvent.KEY_LOCATION_UNKNOWN)
            locationString += "unknown";
        }
        *...//Display information about the KeyEvent...*
    }
}

//*...where member variables are declared...*
private DefaultListModel listModel;
...
//Create and populate the list model
listModel = new DefaultListModel();
...
listModel.addListDataListener(new MyListDataListener());
class MyListDataListener implements ListDataListener {
    public void contentsChanged(ListDataEvent e) {
        log.append("contentsChanged: " + e.getIndex0() +
                   ", " + e.getIndex1() + newline);
    }
    public void intervalAdded(ListDataEvent e) {
        log.append("intervalAdded: " + e.getIndex0() +
                   ", " + e.getIndex1() + newline);
    }
    public void intervalRemoved(ListDataEvent e) {
        log.append("intervalRemoved: " + e.getIndex0() +
                   ", " + e.getIndex1() + newline);
    }
} 

*...//where the member variables are defined*
JList list;
    *...//in the init method:*
    listSelectionModel = list.getSelectionModel();
    listSelectionModel.addListSelectionListener(
                            new SharedListSelectionHandler());
    ...

class SharedListSelectionHandler implements ListSelectionListener {
    public void valueChanged(ListSelectionEvent e) {
        ListSelectionModel lsm = (ListSelectionModel)e.getSource();
        int firstIndex = e.getFirstIndex();
        int lastIndex = e.getLastIndex();
        boolean isAdjusting = e.getValueIsAdjusting();
        output.append("Event for indexes "
                      + firstIndex + " - " + lastIndex
                      + "; isAdjusting is " + isAdjusting
                      + "; selected indexes:");
        if (lsm.isSelectionEmpty()) {
            output.append(" <none>");
        } else {
            // Find out which indexes are selected.
            int minIndex = lsm.getMinSelectionIndex();
            int maxIndex = lsm.getMaxSelectionIndex();
            for (int i = minIndex; i <= maxIndex; i++) {
                if (lsm.isSelectedIndex(i)) {
                    output.append(" " + i);
                }
            }
        }
        output.append(newline);
    }
}

public class MouseEventDemo ... implements MouseListener {
        *//where initialization occurs:*
        //Register for mouse events on blankArea and the panel.
        blankArea.addMouseListener(this);
        addMouseListener(this);
    ...
    public void mousePressed(MouseEvent e) {
       saySomething("Mouse pressed; # of clicks: "
                    + e.getClickCount(), e);
    }
    public void mouseReleased(MouseEvent e) {
       saySomething("Mouse released; # of clicks: "
                    + e.getClickCount(), e);
    }
    public void mouseEntered(MouseEvent e) {
       saySomething("Mouse entered", e);
    }
    public void mouseExited(MouseEvent e) {
       saySomething("Mouse exited", e);
    }
    public void mouseClicked(MouseEvent e) {
       saySomething("Mouse clicked (# of clicks: "
                    + e.getClickCount() + ")", e);
    }
    void saySomething(String eventDescription, MouseEvent e) {
        textArea.append(eventDescription + " detected on "
                        + e.getComponent().getClass().getName()
                        + "." + newline);
    }
}