How to create a circular progress component

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

Code

class ProgressCircleUI extends BasicProgressBarUI {
  @Override public Dimension getPreferredSize(JComponent c) {
    Dimension d = super.getPreferredSize(c);
    int v = Math.max(d.width, d.height);
    d.setSize(v, v);
    return d;
  }

  @Override public void paint(Graphics g, JComponent c) {
    Insets b = progressBar.getInsets(); // area for border
    int barRectWidth  = progressBar.getWidth()  - b.right - b.left;
    int barRectHeight = progressBar.getHeight() - b.top - b.bottom;
    if (barRectWidth <= 0 || barRectHeight <= 0) {
      return;
    }

    // draw the cells
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                        RenderingHints.VALUE_ANTIALIAS_ON);
    double degree = 360 * progressBar.getPercentComplete();
    double sz = Math.min(barRectWidth, barRectHeight);
    double cx = b.left + barRectWidth  * .5;
    double cy = b.top  + barRectHeight * .5;
    double or = sz * .5;
    double ir = or * .5; //or - 20;
    Shape inner  = new Ellipse2D.Double(cx - ir, cy - ir, ir * 2, ir * 2);
    Shape outer  = new Ellipse2D.Double(cx - or, cy - or, sz, sz);
    Shape sector = new Arc2D.Double(
        cx - or, cy - or, sz, sz, 90 - degree, degree, Arc2D.PIE);

    Area foreground = new Area(sector);
    Area background = new Area(outer);
    Area hole = new Area(inner);

    foreground.subtract(hole);
    background.subtract(hole);

    g2.setPaint(new Color(0xDDDDDD));
    g2.fill(background);

    g2.setPaint(progressBar.getForeground());
    g2.fill(foreground);
    g2.dispose();

    // Deal with possible text painting
    if (progressBar.isStringPainted()) {
      paintString(g, b.left, b.top, barRectWidth, barRectHeight, 0, b);
    }
  }
}

// ...
JProgressBar progress = new JProgressBar();
progress.setUI(new ProgressCircleUI());
progress.setBorder(BorderFactory.createEmptyBorder(8, 8, 8, 8));
progress.setStringPainted(true);
progress.setFont(progress.getFont().deriveFont(24f));
progress.setForeground(Color.ORANGE);

(new Timer(50, e -> {
  int iv = Math.min(100, progress.getValue() + 1);
  progress.setValue(iv);
})).start();

References

• How to create a circular progress component(Japanese)