jdk7 增加了一個JLayer，用于在控件上方繪制一個新的圖層。當然jdk6里只要在paint里也能做到，不過新特性方便了很多，最少你可以方便的為Jdk代碼添加這些新特性。
public class Diva {
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() { createUI(); } }); }
public static void createUI() {
JFrame f = new JFrame ("Diva"); LayerUI<JPanel> layerUI = new SpotlightLayerUI();
JPanel panel = createPanel(); JLayer<JPanel> jlayer = new JLayer<JPanel>(panel, layerUI);
f.add (jlayer); f.setSize(300, 200);
f.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
f.setLocationRelativeTo (null); f.setVisible (true); }
private static JPanel createPanel() { JPanel p = new JPanel();
ButtonGroup entreeGroup = new ButtonGroup(); JRadioButton radioButton;
p.add(radioButton = new JRadioButton("Beef", true)); entreeGroup.add(radioButton);
p.add(radioButton = new JRadioButton("Chicken")); entreeGroup.add(radioButton);
p.add(radioButton = new JRadioButton("Vegetable")); entreeGroup.add(radioButton);
p.add(new JCheckBox("Ketchup")); p.add(new JCheckBox("Mustard"));
p.add(new JCheckBox("Pickles")); p.add(new JLabel("Special requests:"));
p.add(new JTextField(20)); JButton orderButton = new JButton("Place Order");
p.add(orderButton); return p; } }
class SpotlightLayerUI extends LayerUI<JPanel> {
private boolean mActive; private int mX, mY;
@Override public void installUI(JComponent c) {
super.installUI(c); JLayer jlayer = (JLayer)c;
jlayer.setLayerEventMask( AWTEvent.MOUSE_EVENT_MASK | AWTEvent.MOUSE_MOTION_EVENT_MASK ); }
@Override public void uninstallUI(JComponent c) { JLayer jlayer = (JLayer)c; jlayer.setLayerEventMask(0);
super.uninstallUI(c); }
@Override public void paint (Graphics g, JComponent c) { Graphics2D g2 = (Graphics2D)g.create();
// Paint the view. super.paint (g2, c); if (mActive) {
// Create a radial gradient, transparent in the middle.
java.awt.geom.Point2D center = new java.awt.geom.Point2D.Float(mX, mY);
float radius = 72; float[] dist = {0.0f, 1.0f};
Color[] colors = {new Color(0.0f, 0.0f, 0.0f, 0.0f), Color.BLACK};
RadialGradientPaint p = new RadialGradientPaint(center, radius, dist, colors);
g2.setPaint(p); g2.setComposite(AlphaComposite.getInstance(
AlphaComposite.SRC_OVER, .6f)); g2.fillRect(0, 0, c.getWidth(), c.getHeight()); }
g2.dispose(); } @Override protected void processMouseEvent(MouseEvent e, JLayer l) {
if (e.getID() == MouseEvent.MOUSE_ENTERED) mActive = true;
if (e.getID() == MouseEvent.MOUSE_EXITED) mActive = false; l.repaint(); }
@Override protected void processMouseMotionEvent(MouseEvent e, JLayer l) {
Point p = SwingUtilities.convertPoint(e.getComponent(), e.getPoint(), l); mX = p.x; mY = p.y; l.repaint(); } }