Adding resume function to stopwatch

Question

I have programmed a simple stopwatch with three functionalities. First, I have a start button to begin the stopwatch , a pause button to pause the stopwatch and finally a re

Answer 1

Conceptually, the idea is, you want to keep track of the "total running" of the stop watch, this is, all the total duration it has been active.

There's a number of ways you might achieve this, one might be to simply keep a running total which is only updated when the stop watch is stopped or paused. The "duration" of the stop watch is then a sum of the "current duration" of the "current" cycle and the "total previous" duration

Something like...

public class StopWatch {
    private LocalDateTime startTime;
    private Duration totalRunTime = Duration.ZERO;

    public void start() {
        startTime = LocalDateTime.now();
    }

    public void stop() {
        Duration runTime = Duration.between(startTime, LocalDateTime.now());
        totalRunTime = totalRunTime.plus(runTime);
        startTime = null;
    }

    public void pause() {
        stop();
    }

    public void resume() {
        start();
    }

    public void reset() {
        stop();
        totalRunTime = Duration.ZERO;
    }

    public boolean isRunning() {
        return startTime != null;
    }

    public Duration getDuration() {
        Duration currentDuration = Duration.ZERO;
        currentDuration = currentDuration.plus(totalRunTime);
        if (isRunning()) {
            Duration runTime = Duration.between(startTime, LocalDateTime.now());
            currentDuration = currentDuration.plus(runTime);
        }
        return currentDuration;
    }
}

Okay, so start and stop are essentially the same as pause and resume, but you get the point.

And, a runnable example...

Now, this example runs a Swing Timer constantly, but the StopWatch can paused and resumed at any time, the point is to demonstrate that the StopWatch is actually working correctly ;)

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.time.Duration;
import java.time.LocalDateTime;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) throws InterruptedException {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private JLabel label;
        private JButton btn;

        private StopWatch stopWatch = new StopWatch();
        private Timer timer;

        public TestPane() {
            label = new JLabel("...");
            btn = new JButton("Start");

            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridwidth = GridBagConstraints.REMAINDER;

            add(label, gbc);
            add(btn, gbc);

            timer = new Timer(500, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    label.setText(Long.toString(stopWatch.getDuration().getSeconds()));
                }
            });
            timer.start();

            btn.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    if (stopWatch.isRunning()) {
                        stopWatch.pause();
                        btn.setText("Start");
                    } else {
                        stopWatch.resume();
                        btn.setText("Pause");
                    }
                }
            });

        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.dispose();
        }

    }

    public class StopWatch {
        private LocalDateTime startTime;
        private Duration totalRunTime = Duration.ZERO;

        public void start() {
            startTime = LocalDateTime.now();
        }

        public void stop() {
            Duration runTime = Duration.between(startTime, LocalDateTime.now());
            totalRunTime = totalRunTime.plus(runTime);
            startTime = null;
        }

        public void pause() {
            stop();
        }

        public void resume() {
            start();
        }

        public void reset() {
            stop();
            totalRunTime = Duration.ZERO;
        }

        public boolean isRunning() {
            return startTime != null;
        }

        public Duration getDuration() {
            Duration currentDuration = Duration.ZERO;
            currentDuration = currentDuration.plus(totalRunTime);
            if (isRunning()) {
                Duration runTime = Duration.between(startTime, LocalDateTime.now());
                currentDuration = currentDuration.plus(runTime);
            }
            return currentDuration;
        }
    }

}