Change the shape of JToolTip to balloon

• download example.jar
• download src.zip
• repository

Code

class BalloonToolTip extends JToolTip {
  private HierarchyListener listener;
  @Override public void updateUI() {
    removeHierarchyListener(listener);
    super.updateUI();
    listener = e -> {
      Component c = e.getComponent();
      boolean b = (e.getChangeFlags() & HierarchyEvent.SHOWING_CHANGED) != 0;
      if (b && c.isShowing()) {
        Window w = SwingUtilities.getWindowAncestor(c);
        if (w != null && w.getType() == Window.Type.POPUP) {
          // Popup$HeavyWeightWindow
          w.setBackground(new Color(0x0, true));
        }
      }
    };
    addHierarchyListener(listener);
    setOpaque(false);
    setBorder(BorderFactory.createEmptyBorder(8, 5, 0, 5));
  }

  @Override public Dimension getPreferredSize() {
    Dimension d = super.getPreferredSize();
    d.height = 28;
    return d;
  }

  @Override public void paintComponent(Graphics g) {
    Shape s = makeBalloonShape();
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                        RenderingHints.VALUE_ANTIALIAS_ON);
    g2.setColor(getBackground());
    g2.fill(s);
    g2.setColor(getForeground());
    g2.draw(s);
    g2.dispose();
    super.paintComponent(g);
  }

  private Shape makeBalloonShape() {
    Insets i = getInsets();
    int w = getWidth() - 1;
    int h = getHeight() - 1;
    int v = i.top / 2;
    Polygon triangle = new Polygon();
    triangle.addPoint(i.left + v + v, 0);
    triangle.addPoint(i.left + v, v);
    triangle.addPoint(i.left + v + v + v, v);
    Area area = new Area(new RoundRectangle2D.Float(
        0, v, w, h - i.bottom - v, i.top, i.top));
    area.add(new Area(triangle));
    return area;
  }
}

//...
JList<String> list = new JList<String>(model) {
  @Override public JToolTip createToolTip() {
    JToolTip tip = new BalloonToolTip();
    tip.setComponent(this);
    return tip;
  }
};

References

• Change the shape of JToolTip to balloon(Japanese)