Creating a Swing Dashboard Widget - Part 2 (Border)

Widgets have nice rounded borders. The LineBorder in the JDK doesn't really cut it: It's not anti-aliased, it draws weird artifacts, and it's tough to have the outside of the border transparent while inside the border is opaque.
While there are separate ways to fix these things, it's fairly easy to write one:

<br />public class RoundedBorder extends AbstractBorder {<br /> private Insets insets;<br /> private Stroke stroke;<br /> private Color strokeColor;<br /> private int arc;<br /> private float strokeWidth;<br /> <br /> /**<br /> * Simple rounded border with no outline<br /> * @param arc<br /> */<br /> public RoundedBorder(int arc) {<br /> this.arc = arc;<br /> int i = (int)(arc / Math.PI) / 2;<br /> insets = new Insets(i, i, i, i);<br /> }<br /><br /> /**<br /> * Rounded border with an outline<br /> * @param arc<br /> * @param strokeWidth width of the outline<br /> * @param color color of the outline<br /> */<br /> public RoundedBorder(int arc, float strokeWidth, Color color) {<br /> this.arc = arc;<br /> int i = (int)((arc / Math.PI) + ((strokeWidth * 2) / (Math.PI)));<br /> insets = new Insets(i, i, i, i);<br /> this.stroke = new BasicStroke(strokeWidth);<br /> this.strokeColor = color;<br /> this.strokeWidth = strokeWidth;<br /> }<br /><br /> public void paintBorder(Component c, Graphics g, int x, int y, int width,<br /> int height) {<br /> Graphics2D g2 = (Graphics2D)g.create();<br /> g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,<br /> RenderingHints.VALUE_ANTIALIAS_ON);<br /><br /> // In real code optimize by preserving the rect between calls<br /> if (stroke != null) {<br /> int i = (int)strokeWidth / 2;<br /> RoundRectangle2D.Float rect =<br /> new RoundRectangle2D.Float(i, i, width - strokeWidth,<br /> height - strokeWidth, arc, arc);<br /> g2.translate(x, y);<br /> g2.setColor(c.getBackground());<br /> g2.fill(rect);<br /><br /> g2.setColor(strokeColor);<br /> g2.setStroke(stroke);<br /> g2.draw(rect);<br /> } else {<br /> RoundRectangle2D.Float rect =<br /> new RoundRectangle2D.Float(0, 0, width, height, arc, arc);<br /> g2.translate(x, y);<br /> g2.setColor(c.getBackground());<br /> g2.fill(rect);<br /> }<br /> }<br /><br /> // boring stuff from here on...<br /><br /> public Insets getBorderInsets(Component c) {<br /> return insets;<br /> }<br /><br /> public Insets getBorderInsets(Component c, Insets insets) {<br /> return insets;<br /> }<br /><br /> public Rectangle getInteriorRectangle(Component c, int x, int y, int width,<br /> int height) {<br /> return getInteriorRectangle(c, this, x, y, width, height);<br /> }<br /><br /> public static Rectangle getInteriorRectangle(Component c, Border b, int x,<br /> int y, int width, int height) {<br /> Insets insets;<br /> if (b != null)<br /> insets = b.getBorderInsets(c);<br /> else<br /> insets = new Insets(0, 0, 0, 0);<br /> return new Rectangle(x + insets.left, y + insets.top,<br /> width - insets.right - insets.left,<br /> height - insets.top - insets.bottom);<br /> }<br />}<br />

As this border does the job of filling the entire background of the component with the component's background color, we can make the actual component transparent and this will leave nice transparent areas outside the curves of the corners. (Opaque components fill their entire bounds with the background color).
The drawback of this is that the border is painted after the component's contents, so custom painting for the widget content must be done in the paint method rather than the paintComponent or it won't show up.