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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 reset button to reset the entire stopwatch.

When I hit the pause button, the stopwatch pauses, say at 10.0 seconds. When I resume the stopwatch (pressing the Start button again), the stopwatch doesn't resume from 10.0 seconds onwards. It resumes from the amount of time I paused and the current time. For example, if I paused for 5 seconds and hit resume, the stopwatch goes from 15.0 seconds onwards.

I am aware there isn't a actual pause function in Swing.Timer. Would there be a way to tackle this so the stopwatch resumes normally?

Any suggestion would be appreciated.

Code:

import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.time.Duration;
import java.time.Instant;
import javax.swing.Timer;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;



public class GuiStopwatch {





 public static void main(String args) {
 JFrame frame = new JFrame("Stopwatch");

 frame.setSize(500, 500);
 frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
 frame.setVisible(true);
 JPanel panel = new JPanel();

 panel.setLayout(null);

 JButton startbtn = new JButton("START"); 
 JButton pausebtn = new JButton("PAUSE");
 JButton reset = new JButton("RESET");
 JLabel time = new JLabel("Time shows here");
 panel.add(startbtn);
 panel.add(pausebtn);
 panel.add(reset);
 panel.add(time);
 startbtn.setBounds(50, 150, 100, 35);
 pausebtn.setBounds(50, 200, 100, 35);
 reset.setBounds(50, 250, 100, 35);
 time.setBounds(50, 350, 100, 35);
 time.setBackground(Color.black);
 time.setForeground(Color.red);
 frame.add(panel);



 Timer timer = new Timer(1,new ActionListener() 
 Instant start = Instant.now();
 @Override
 public void actionPerformed(ActionEvent e) 


 time.setText( Duration.between(start, Instant.now()).getSeconds() + ":" + Duration.between(start, Instant.now()).getNano() );


 
 );



 startbtn.addActionListener(new ActionListener() 


 @Override
 public void actionPerformed(ActionEvent e) 





 timer.start();




 
 );



 pausebtn.addActionListener(new ActionListener() 

 @Override
 public void actionPerformed(ActionEvent e) 

 timer.stop();

 
 );



 reset.addActionListener(new ActionListener() 

 @Override
 public void actionPerformed(ActionEvent e) 
 time.setText("0:0");

 
 );

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() InstantiationException 
 );
 

 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;