Clock for System Tray.

PacificTime.java

package com.mm.exp.clock;

import java.awt.*;
import java.awt.geom.AffineTransform;
import java.awt.geom.Arc2D;
import java.awt.geom.Line2D;
import java.awt.image.BufferedImage;
import java.text.DateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.TimeZone;

public final class PacificTime {
    private static final TimeZone TIME_ZONE = TimeZone.getTimeZone("PST");
    private final Dimension center;
    private Line2D hourHand;
    private Line2D minuteHand;
    private Line2D hourTic;
    private volatile Calendar cal = new GregorianCalendar();
    private final Shape circle;
    private final Stroke half = new BasicStroke(0.5f);
    private final Stroke one = new BasicStroke(1.0f);
    private final DateFormat format = DateFormat.getTimeInstance(DateFormat.SHORT);
    private static TrayIcon icon;
    private static Dimension size;
    private static final double twoPi = 2.0 * Math.PI;
    private static final long delay = 60000L;
    private static final Color transparent = new Color(0, 0, 0, 0);

    public static void main(String[] args) throws AWTException {
        SystemTray systemTray = SystemTray.getSystemTray();
        size = systemTray.getTrayIconSize();
        PacificTime pacificTime = new PacificTime();
        Image image = makeImage(pacificTime);
        pacificTime.previousImage = image;
        icon = new TrayIcon(image);
        icon.setToolTip(pacificTime.getToolTipText());
        addMenu(icon);
        systemTray.add(icon);
        startThread(pacificTime);
    }

    private PacificTime() {
        center = new Dimension(size.width/2, size.height/2);
        circle = new Arc2D.Double(1.0, 1.0, size.getWidth()-2.0, size.getHeight()-2.0, 0.0, 360.0, Arc2D.OPEN);
        double minHandLength = ((double) (size.height - 2) / 2.0) * 0.9;
        double hourHandLength = minHandLength * 0.7;
        hourHand = new Line2D.Double(0.0, 0.0, 0.0, -hourHandLength);
        minuteHand = new Line2D.Double(0.0, 0.0, 0.0, -minHandLength);
        hourTic = new Line2D.Double(0.0, minHandLength, 0.0, (size.getHeight()/2.0));

        cal.setTimeZone(TIME_ZONE);
        format.setTimeZone(TIME_ZONE);
    } 

    private void paintIcon(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL, RenderingHints.VALUE_STROKE_PURE);

        g2.setColor(transparent);
        g2.fillRect(0, 0, getIconWidth(), getIconHeight());
        g2.setColor(Color.WHITE);
        g2.fill(circle);

        g2.setStroke(half);
        g2.setColor(Color.lightGray);
        g2.draw(circle);

        int hour = cal.get(Calendar.HOUR);
        int min = cal.get(Calendar.MINUTE);
        double fullHour = ((double) hour + ((double) min / 60.0))/12.0;
        double fullMinute = (double) min / 60.0;
        double minAngle = fullMinute * twoPi;
        double hourAngle = fullHour * twoPi;
        drawHands(g2, minAngle, hourAngle);
    }
    
    private static void addMenu(TrayIcon icon) {
        PopupMenu popupMenu = new PopupMenu();
        icon.setPopupMenu(popupMenu);

        MenuItem exitItem = new MenuItem("Exit");
        exitItem.addActionListener((e) -> SystemTray.getSystemTray().remove(icon));
        popupMenu.add(exitItem);
    }
    
    private void drawHands(Graphics2D g2, double minAngle, double hourAngle) {
        AffineTransform savedTransform = g2.getTransform();
        g2.translate(center.width, center.height);

        g2.setStroke(half);
        g2.setColor(Color.BLACK);
        double hourTicAngle = twoPi/12.0;
        for (int ii=0; ii<12; ++ii) {
            g2.draw(hourTic);
            g2.rotate(hourTicAngle);
        }
        g2.rotate(minAngle);
        g2.setStroke(one);
        g2.draw(minuteHand);
        g2.rotate(hourAngle - minAngle);
        g2.setColor(Color.RED);
        g2.draw(hourHand);
        g2.setTransform(savedTransform);
    }

    private Image previousImage = null;
    private static Image makeImage(PacificTime icon) {
        Image image = new BufferedImage(getIconWidth(), getIconHeight(), BufferedImage.TYPE_INT_ARGB);
        Graphics g2 = image.getGraphics();
        icon.paintIcon(g2);
        g2.dispose();
        return image;
    }

    private String getToolTipText() {
        Date date = new Date();
        cal.setTime(date);
        return format.format(cal.getTime());
    }

    private static int getIconWidth() {
        return size.width;
    }

    private static int getIconHeight() {
        return size.height;
    }

    private static void startThread(final PacificTime pacificTime) {
        Thread thread = new Thread(pacificTime::timerLoop);
        thread.setDaemon(true);
        thread.start();
    }

    private void timerLoop() {
        //noinspection InfiniteLoopStatement
        while (true) {
            long delta = delay - (System.currentTimeMillis() % delay); // millis remaining in current minute
            try {
                //noinspection BusyWait
                Thread.sleep(delta);
            } catch (InterruptedException ignored) { }

            icon.setToolTip(getToolTipText());
            Image prior = previousImage;
            Image current = makeImage(this);
            icon.setImage(current);
            prior.flush();
            previousImage = current;
        }
    }
}