import java.awt.*; import java.awt.event.*; import javax.swing.*; /** * This applet demonstrates Focus events and Key events. A colored square * is drawn on the applet. By pressing the arrow keys, the user can move * the square up, down, left, or right. By pressing the keys * R, G, B, or K, the user can change the color of the square to red, * green, blue, or black, respectively. Of course, none of the keys * will have any effect if the applet does not have the keyboard input * focus. The applet changes appearance when it has the input focus. * A cyan-colored border is drawn around it. When it does not have * the input focus, the message "Click to activate" is displayed * and the border is gray. *

This class contains a main() routine; when it is run as a stand-alone * application, the same JPanel that is used in the applet is shown in a * window instead. The JPanel is defined using a nested subclass. */ public class KeyboardAndFocusDemo extends JApplet { /** * The main program just opens a window that shows an object of type * ContentPanel -- a nested class that is defined later in this class. */ public static void main(String[] args) { JFrame window = new JFrame("Keyboard and Focus Demo"); window.setContentPane( new ContentPanel() ); window.setSize(300,300); window.setLocation(100,100); window.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); window.setVisible(true); } /** * The init() method of the applet just sets the content pane * of the applet to be a panel of type ContentPane, a nested class * that is defined below, which does all the work. */ public void init() { setContentPane( new ContentPanel() ); } /** * Defines the content pane that is used in both the applet and * the stand-alone application version of this program. The * panel displays a colored square that can be moved by the user, * by pressing the arrow keys. The color of the square can be * changed by pressing the R, G, B, and K keys. The panel also * displays a border and a message. */ public static class ContentPanel extends JPanel implements KeyListener, FocusListener, MouseListener { // (Note: MouseListener is implemented only so that // the applet can request the input focus when // the user clicks on it.) private static final int SQUARE_SIZE = 40; // Length of side of square. private Color squareColor; // The color of the square. private int squareTop, squareLeft; // Coordinates corner of square. /** * The constructor sets the initial position and color of the square * and registers itself to act as a listener for Key, Focus, and * Mouse events. */ public ContentPanel() { squareTop = 100; // Initial position of top-left corner of square. squareLeft = 100; squareColor = Color.RED; // Initial color of square. setBackground(Color.WHITE); addKeyListener(this); // Set up event listening. addFocusListener(this); addMouseListener(this); } // end init(); /** * Draws a border, square, and message in the panel. The message and * the color of the border depend on whether or not the pane has * the input focus. */ public void paintComponent(Graphics g) { super.paintComponent(g); // Fills the panel with its // background color, which is white. /* Draw a 3-pixel border, colored cyan if the applet has the keyboard focus, or in light gray if it does not. */ if (hasFocus()) g.setColor(Color.CYAN); else g.setColor(Color.LIGHT_GRAY); int width = getSize().width; // Width of the applet. int height = getSize().height; // Height of the applet. g.drawRect(0,0,width-1,height-1); g.drawRect(1,1,width-3,height-3); g.drawRect(2,2,width-5,height-5); /* Draw the square. */ g.setColor(squareColor); g.fillRect(squareLeft, squareTop, SQUARE_SIZE, SQUARE_SIZE); /* Print a message that depends on whether the panel has the focus. */ g.setColor(Color.magenta); if (hasFocus()) { g.drawString("Arrow Keys Move Square",7,20); g.drawString("K, R, G, B Change Color",7,40); } else g.drawString("Click to activate",7,20); } // end paintComponent() // ------------------- Event handling methods ---------------------- /** * This will be called when the panel gains the input focus. It just * calls repaint(). The panel will be redrawn with a cyan-colored border * and with a message about keyboard input. */ public void focusGained(FocusEvent evt) { repaint(); // redraw with cyan border } /** * This will be called when the panel loses the input focus. It just * calls repaint(). The panel will be redrawn with a gray-colored border * and with the message "Click to activate." */ public void focusLost(FocusEvent evt) { repaint(); // redraw without cyan border } /** * This method is called when the user types a character on the keyboard * while the panel has the input focus. If the character is R, G, B, or K * (or the corresponding lower case characters), then the color of the * square is changed to red, green, blue, or black, respectively. */ public void keyTyped(KeyEvent evt) { char ch = evt.getKeyChar(); // The character typed. if (ch == 'B' || ch == 'b') { squareColor = Color.BLUE; repaint(); // Redraw panel with new color. } else if (ch == 'G' || ch == 'g') { squareColor = Color.GREEN; repaint(); } else if (ch == 'R' || ch == 'r') { squareColor = Color.RED; repaint(); } else if (ch == 'K' || ch == 'k') { squareColor = Color.BLACK; repaint(); } } // end keyTyped() /** * This is called each time the user presses a key while the panel has * the input focus. If the key pressed was one of the arrow keys, * the square is moved (except that it is not allowed to move off the * edge of the panel). */ public void keyPressed(KeyEvent evt) { int key = evt.getKeyCode(); // keyboard code for the pressed key if (key == KeyEvent.VK_LEFT) { // left arrow key squareLeft -= 8; if (squareLeft < 3) squareLeft = 3; repaint(); } else if (key == KeyEvent.VK_RIGHT) { // right arrow key squareLeft += 8; if (squareLeft > getWidth() - 3 - SQUARE_SIZE) squareLeft = getWidth() - 3 - SQUARE_SIZE; repaint(); } else if (key == KeyEvent.VK_UP) { // up arrow key squareTop -= 8; if (squareTop < 3) squareTop = 3; repaint(); } else if (key == KeyEvent.VK_DOWN) { // down arrow key squareTop += 8; if (squareTop > getHeight() - 3 - SQUARE_SIZE) squareTop = getHeight() - 3 - SQUARE_SIZE; repaint(); } } // end keyPressed() /** * This is called each time the user releases a key while the panel * has the input focus. In this class, it does nothing, but it is * required to be here by the KeyListener interface. */ public void keyReleased(KeyEvent evt) { } /** * This is called when the user clicks the panel with the mouse. * It just requests that the input focus be given to this panel. */ public void mousePressed(MouseEvent evt) { requestFocus(); } public void mouseEntered(MouseEvent evt) { } // Required by the public void mouseExited(MouseEvent evt) { } // MouseListener public void mouseReleased(MouseEvent evt) { } // interface. public void mouseClicked(MouseEvent evt) { } } // end nested class ContentPanel } // end class KeyboardAndFocusDemo