在Java用户界面上显示一个实时指针时钟

以下是一个使用Java Swing实现的实时指针时钟的示例代码：

import javax.swing.*;
import java.awt.*;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class PointerClock extends JFrame {

    private JPanel contentPane;
    private ClockPanel clockPanel;

    public PointerClock() {
        setTitle("Pointer Clock");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 400, 400);
        contentPane = new JPanel();
        contentPane.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);

        clockPanel = new ClockPanel();
        contentPane.add(clockPanel, BorderLayout.CENTER);

        setVisible(true);
    }

    public static void main(String[] args) {
        new PointerClock();
    }

    private class ClockPanel extends JPanel {

        private int centerX, centerY;
        private int radius;
        private int hourHandLength, minuteHandLength, secondHandLength;
        private int hourHandWidth, minuteHandWidth, secondHandWidth;
        private Color hourHandColor, minuteHandColor, secondHandColor;

        public ClockPanel() {
            setOpaque(false);
            Timer timer = new Timer(1000, e -> repaint());
            timer.start();
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            int width = getWidth();
            int height = getHeight();
            int size = Math.min(width, height);

            centerX = width / 2;
            centerY = height / 2;
            radius = size / 2 - 10;

            hourHandLength = (int) (radius * 0.5);
            minuteHandLength = (int) (radius * 0.7);
            secondHandLength = (int) (radius * 0.9);

            hourHandWidth = 6;
            minuteHandWidth = 4;
            secondHandWidth = 2;

            hourHandColor = Color.BLACK;
            minuteHandColor = Color.BLACK;
            secondHandColor = Color.RED;

            Graphics2D g2d = (Graphics2D) g;
            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

            drawClockFace(g2d);
            drawHourHand(g2d);
            drawMinuteHand(g2d);
            drawSecondHand(g2d);
        }

        private void drawClockFace(Graphics2D g2d) {
            g2d.setColor(Color.WHITE);
            g2d.fillOval(centerX - radius, centerY - radius, radius * 2, radius * 2);
            g2d.setColor(Color.BLACK);
            g2d.drawOval(centerX - radius, centerY - radius, radius * 2, radius * 2);

            for (int i = 1; i <= 12; i++) {
                double angle = Math.PI / 6 * i;
                int x = (int) (centerX + Math.sin(angle) * (radius - 20));
                int y = (int) (centerY - Math.cos(angle) * (radius - 20));
                g2d.drawString(String.valueOf(i), x, y);
            }
        }

        private void drawHourHand(Graphics2D g2d) {
            Calendar calendar = Calendar.getInstance();
            int hour = calendar.get(Calendar.HOUR);
            int minute = calendar.get(Calendar.MINUTE);
            int second = calendar.get(Calendar.SECOND);

            double angle = Math.PI / 6 * hour + Math.PI / 360 * minute + Math.PI / 21600 * second;
            int x = (int) (centerX + Math.sin(angle) * hourHandLength);
            int y = (int) (centerY - Math.cos(angle) * hourHandLength);

            g2d.setColor(hourHandColor);
            g2d.setStroke(new BasicStroke(hourHandWidth, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
            g2d.drawLine(centerX, centerY, x, y);
        }

        private void drawMinuteHand(Graphics2D g2d) {
            Calendar calendar = Calendar.getInstance();
            int minute = calendar.get(Calendar.MINUTE);
            int second = calendar.get(Calendar.SECOND);

            double angle = Math.PI / 30 * minute + Math.PI / 1800 * second;
            int x = (int) (centerX + Math.sin(angle) * minuteHandLength);
            int y = (int) (centerY - Math.cos(angle) * minuteHandLength);

            g2d.setColor(minuteHandColor);
            g2d.setStroke(new BasicStroke(minuteHandWidth, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
            g2d.drawLine(centerX, centerY, x, y);
        }

        private void drawSecondHand(Graphics2D g2d) {
            Calendar calendar = Calendar.getInstance();
            int second = calendar.get(Calendar.SECOND);

            double angle = Math.PI / 30 * second;
            int x = (int) (centerX + Math.sin(angle) * secondHandLength);
            int y = (int) (centerY - Math.cos(angle) * secondHandLength);

            g2d.setColor(secondHandColor);
            g2d.setStroke(new BasicStroke(secondHandWidth, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
            g2d.drawLine(centerX, centerY, x, y);
        }
    }
}

该代码使用了Java Swing中的JFrame和JPanel来创建用户界面，并使用Graphics2D类来绘制指针时钟。实时更新时钟的功能是通过使用Java定时器实现的。在绘制时钟的过程中，该代码使用了Calendar类来获取当前时间，并通过一些基本的几何计算来计算时针、分针和秒针的位置和角度。最终绘制时针、分针和秒针时，该代码使用了Graphics2D类的一些基本绘图方法来绘制它们。