我可以想到两种方法.第一种是生成一个表示方形外边缘和圆形内边缘的Shape.

第二种方法是使用AlphaComposite生成掩码结果.

public class TestMask {

public static void main(String[] args) {

new TestMask();

}

public TestMask() {

EventQueue.invokeLater(new Runnable() {

@Override

public void run() {

try {

UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {

}

JFrame frame = new JFrame("Testing");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setLayout(new BorderLayout());

frame.add(new MaskedPane());

frame.pack();

frame.setLocationRelativeTo(null);

frame.setVisible(true);

}

});

}

public class MaskedPane extends JPanel {

public MaskedPane() {

setBackground(Color.RED);

}

@Override

public Dimension getPreferredSize() {

return new Dimension(200, 200);

}

@Override

protected void paintComponent(Graphics g) {

super.paintComponent(g);

BufferedImage outter = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);

Graphics2D g2d = outter.createGraphics();

g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

g2d.setColor(Color.BLACK);

g2d.fillRect(0, 0, getWidth(), getHeight());

g2d.dispose();

BufferedImage inner = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);

g2d = inner.createGraphics();

g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

g2d.setColor(Color.BLACK);

g2d.fillRoundRect(10, 10, getWidth() - 20, getHeight() - 20, 20, 20);

g2d.dispose();

BufferedImage masked = applyMask(outter, inner, AlphaComposite.DST_OUT);

g.drawImage(masked, 0, 0, this);

}

public BufferedImage applyMask(BufferedImage sourceImage, BufferedImage maskImage, int method) {

BufferedImage maskedImage = null;

if (sourceImage != null) {

int width = maskImage.getWidth();

int height = maskImage.getHeight();

maskedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);

Graphics2D mg = maskedImage.createGraphics();

int x = (width - sourceImage.getWidth()) / 2;

int y = (height - sourceImage.getHeight()) / 2;

mg.drawImage(sourceImage, x, y, null);

mg.setComposite(AlphaComposite.getInstance(method));

mg.drawImage(maskImage, 0, 0, null);

mg.dispose();

}

return maskedImage;

}

public BufferedImage applyMask(BufferedImage sourceImage, BufferedImage maskImage) {

return (BufferedImage) applyMask(sourceImage, maskImage, AlphaComposite.DST_IN);

}

}

}

更新了Shape示例

终于有时间敲出一个……

public class TestMask {

public static void main(String[] args) {

new TestMask();

}

public TestMask() {

EventQueue.invokeLater(new Runnable() {

@Override

public void run() {

try {

UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {

}

JFrame frame = new JFrame("Testing");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setLayout(new BorderLayout());

frame.add(new ShapedPane());

frame.pack();

frame.setLocationRelativeTo(null);

frame.setVisible(true);

}

});

}

public class ShapedPane extends JPanel {

public ShapedPane() {

setBackground(Color.GREEN);

}

@Override

public Dimension getPreferredSize() {

return new Dimension(200, 200);

}

@Override

protected void paintComponent(Graphics g) {

super.paintComponent(g);

Graphics2D g2d = (Graphics2D) g.create();

g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

g2d.setColor(Color.BLACK);

g2d.fill(new RounedFrame(getWidth(), getHeight(), 10, 20));

g2d.dispose();

}

}

public class RounedFrame extends Path2D.Float {

public RounedFrame(float width, float height, float thickness, float radius) {

moveTo(0, 0);

lineTo(width, 0);

lineTo(width, height);

lineTo(0, height);

lineTo(0, 0);

float innerWidth = width - thickness;

float innerHeight = height - thickness;

moveTo(thickness + radius, thickness);

lineTo(innerWidth - radius, thickness);

curveTo(innerWidth, thickness, innerWidth, thickness, innerWidth, thickness + radius);

lineTo(innerWidth, innerHeight - radius);

curveTo(innerWidth, innerHeight, innerWidth, innerHeight, innerWidth - radius, innerHeight);

lineTo(thickness + radius, innerHeight);

curveTo(thickness, innerHeight, thickness, innerHeight, thickness, innerHeight - radius);

lineTo(thickness, thickness + radius);

curveTo(thickness, thickness, thickness, thickness, thickness + radius, thickness);

closePath();

setWindingRule(WIND_EVEN_ODD);

}

}

}

更新

根据Andrew的评论,您可以使用Area简化形状示例的使用

您可以使用以下示例替换上面示例中的paintComponent …

@Override

protected void paintComponent(Graphics g) {

super.paintComponent(g);

Area area = new Area(new Rectangle(0, 0, getWidth(), getHeight()));

area.subtract(new Area(new RoundRectangle2D.Float(10, 10, getWidth() - 20, getHeight() - 20, 20, 20)));

Graphics2D g2d = (Graphics2D) g.create();

g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

g2d.setColor(Color.BLACK);

g2d.fill(area);

g2d.dispose();

}

这更简单：D