import java.awt.*; import java.awt.event.*; import javax.swing.*; /** * This program demonstrates Focus events and Key events. A colored square * is drawn on the panel. 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. The panel 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. The panel should have focus * whenever the program window is active. * This class contains a main() routine so that it can be run as a program * @author David J. Eck */ public class KeyboardAndFocusDemo extends JPanel { /** * The main program just opens a window that shows an object of type * KeyboardAndFocusDemo. Note that it requests focus for the panel. * This has to be done after the window is made visible for it to have * any effect. */ public static void main(String[] args) { JFrame window = new JFrame("Keyboard and Focus Demo"); KeyboardAndFocusDemo content = new KeyboardAndFocusDemo(); window.setContentPane( content ); window.setSize(400,400); window.setLocation(100,100); window.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); window.setVisible(true); content.requestFocusInWindow(); } //------------------------------------------------------------------------ /** * This nested class is used to define a keyboard and focus listener that * will listen for events on the panel. */ private class Listener implements KeyListener, FocusListener { /** * 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) { } } // end nested class Listener // ---------------------------------------------------------------------------- private static final int SQUARE_SIZE = 50; // 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 KeyboardAndFocusDemo() { squareTop = 100; // Initial position of top-left corner of square. squareLeft = 100; squareColor = Color.RED; // Initial color of square. setBackground(Color.WHITE); Listener listener = new Listener(); // listener for keyboard and focus events addKeyListener(listener); // Listen for key events from this panel. addFocusListener(listener); // Listen for focus evens from this panel. } // end constructor /** * 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 panel 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 panel. int height = getSize().height; // Height of the panel. 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() } // end class KeyboardAndFocusDemo