Pause and resume for Swing Timer does not work properly

Question

My program is a memory game. Whenever a tile is clicked, the timer would start. I am trying to create a menu for pause and resume of the Swing Timer. The pause works just fine; however, the problem I am experiencing is whenever I resume the timer after the pause, it would skip four seconds instead of continuing the timer The specific methods for the timer is posted below the whole program code. Here's what I currently have:

import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.Arrays;
import javax.swing.*;
import java.util.Collections;
import java.util.Calendar;
import java.time.*;

public class MemoryGame implements ActionListener {

private Timer cdTimer;  //Count down timer of 1.5 secs for unmatched pairs
private Timer swTimer;  //Main timer for the game

private int count = 0;
private long start = Calendar.getInstance().getTimeInMillis();
private long now;
private long elapsed;
boolean match = false;  //Determine if the cdTimer is running or not

private JToggleButton[] buttons;
private JToggleButton first;  //Variable for the first button to match
private JLabel time;  //Label to hold the 

private JMenuItem pause;
private JMenuItem resume;

ArrayList<ImageIcon> iconList = new ArrayList();
ArrayList<JToggleButton> retireButton = new ArrayList();  
ImageIcon icon = new ImageIcon("MemoryGame.png");

public MemoryGame() {

    JFrame jfrm = new JFrame("Memory Game");

    jfrm.setSize(1000, 1000);

    jfrm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    jfrm.setIconImage(icon.getImage());

    time = new JLabel("Elapsed time is 00:00:00");

    GridLayout layout = new GridLayout(3,4);

    JPanel gamePanel = new JPanel();
    gamePanel.setLayout(layout);

    createIcons();  //set icons for the tiles

    buttons = new JToggleButton[12];

    for(int i = 0; i < buttons.length; i++) {
        JToggleButton btn = new JToggleButton(icon);

        buttons[i] = btn;

        buttons[i].addActionListener(this);

        gamePanel.add(buttons[i]);   
    }

    Collections.shuffle(Arrays.asList(buttons));
    Collections.shuffle(iconList);

    jfrm.add(gamePanel, BorderLayout.CENTER);
    time.setHorizontalAlignment(JLabel.CENTER);
    time.setVerticalAlignment(JLabel.CENTER);
    jfrm.add(time, BorderLayout.NORTH);

    //Create menus
    JMenuBar jm = new JMenuBar();
    JMenu action = new JMenu("Action");
    action.setMnemonic(KeyEvent.VK_A);

    JMenu gameTimer = new JMenu("Game Timer");
    gameTimer.setMnemonic(KeyEvent.VK_T);
    pause = new JMenuItem("Pause", KeyEvent.VK_P);
    pause.setAccelerator(KeyStroke.getKeyStroke("control P"));
    pause.setEnabled(false);
    pause.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            elapsed += now;
            swTimer.stop();
        }
    });
    resume = new JMenuItem("Resume", KeyEvent.VK_R);
    resume.setAccelerator(KeyStroke.getKeyStroke("control R"));
    resume.setEnabled(false);
    resume.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            timerContinue();
        }
    });
    gameTimer.add(pause);
    gameTimer.add(resume);
    action.add(gameTimer);

    JMenuItem reveal = new JMenuItem("Reveal", KeyEvent.VK_R);
    reveal.addActionListener(this);
    action.add(reveal);
    action.addSeparator();

    JMenuItem exit = new JMenuItem("Exit", KeyEvent.VK_X);
    exit.addActionListener(this);
    action.add(exit);

    JMenu help = new JMenu("Help");
    help.setMnemonic(KeyEvent.VK_H);
    JMenuItem viewHelp = new JMenuItem("View Help...", 
KeyEvent.VK_H);
    viewHelp.addActionListener(this);
    help.add(viewHelp);
    help.addSeparator();
    JMenuItem about = new JMenuItem("About", KeyEvent.VK_A);
    about.addActionListener(this);
    help.add(about);

    jm.add(action);
    jm.add(help);
    jfrm.setJMenuBar(jm);

    jfrm.setLocationRelativeTo(null);

    jfrm.setVisible(true);
}

public void actionPerformed(ActionEvent e){
    //this if makes sure the timer does not restart everytime a button is clicked
    if(retireButton.size() == 0){
        timerStart();
    }     

    if(swTimer.isRunning()){
        pause.setEnabled(true);
        resume.setEnabled(true);
    }

    //this if makes sure no button will be input during the 1.5 secs delay
    if(match == false){
        JToggleButton btn = (JToggleButton)e.getSource(); //take in button
        setIcon(btn);  
        resetIcon(btn);
        //this if makes btn equals the first button if it is null
        if(first == null){
            first = btn;
            return;
        }

        matching(first, btn);

        first = null;
    }
}

public void updateTime(){
    long temp = Calendar.getInstance().getTimeInMillis();
    time.setText("Elapsed time is " + formatTime((long) (temp - start)));
    now = temp - start;    
}

public void continueTime(){
    long temp = Calendar.getInstance().getTimeInMillis();
    time.setText("Elapsed time is " + formatTime((long) (temp - start)));
}

private void timerContinue(){
    ActionListener timerAL = new ActionListener(){
        public void actionPerformed(ActionEvent e){
            continueTime();
        }
    };

    //stop the timer if it is still running
    if (swTimer != null && swTimer.isRunning()) {
        swTimer.stop();
    }

    swTimer = new Timer(1000, timerAL);
    swTimer.setInitialDelay(0);
    swTimer.start();
}

public static String formatTime(long ms){
    long millis = ms % 1000;
    long x = ms / 1000;
    long seconds = x % 60;
    x /= 60;
    long minutes = x % 60;
    x /= 60;
    long hours = x % 24;

    return String.format("%02d:%02d:%02d", hours, minutes, seconds);
}

//Method to reset the button to game image when it is clicked for a second time
private void resetIcon(JToggleButton btn){
    if(!btn.isSelected()){
        btn.setIcon(icon);
    }
}

private void timerStart(){
    ActionListener timerAL = new ActionListener(){
        public void actionPerformed(ActionEvent e){
            updateTime();
        }
    };

    //stop the timer if it is still running
    if (swTimer != null && swTimer.isRunning()) {
        swTimer.stop();
    }

    swTimer = new Timer(1000, timerAL);
    swTimer.setInitialDelay(0);
    swTimer.start();
}

private void timerStop(){
    //if all 12 buttons are matched, then stop the timer
    if(retireButton.size() == 12){
        long stop = Calendar.getInstance().getTimeInMillis();
        time.setText("You finished in " + formatTime((long)(stop-start)));
        swTimer.stop();
    }
}

//set the icons for the tiles
private void setIcon(JToggleButton btn) {
    if(btn == buttons[0] || btn == buttons[1])
        btn.setIcon(iconList.get(0)); 

    else if(btn == buttons[2] || btn == buttons[3])
        btn.setIcon(iconList.get(1));

    else if(btn == buttons[4] || btn == buttons[5])
        btn.setIcon(iconList.get(2));

    else if(btn == buttons[6] || btn == buttons[7])
        btn.setIcon(iconList.get(3));

    else if(btn == buttons[8] || btn == buttons[9])
        btn.setIcon(iconList.get(4));

    else if(btn == buttons[10] || btn == buttons[11])
        btn.setIcon(iconList.get(5));
}

//match the two input buttons
private void matching(JToggleButton btn, JToggleButton btn2){
    if(btn.isSelected()){
        if(btn2.isSelected()){
            buttonDisable(btn, btn2); //disable all buttons besides btn, and btn2
            if(!btn.getIcon().toString().equals(btn2.getIcon().toString())){
                startTime(1, btn, btn2);  //start the 1.5 secs countdown
            }
            else {
                retirePair(btn, btn2);
                timerStop();
                buttonEnable(btn, btn2);
            }
        }
    }   
}

private void startTime(int countPassed, JToggleButton btn, JToggleButton btn2){
    ActionListener action = new ActionListener(){
        public void actionPerformed(ActionEvent e){
            if(count == 0){
                cdTimer.stop();
                match = false;  //resets match
                unflipPair(btn, btn2);  //reset tile to game image again
                buttonEnable(btn, btn2);
            }
            else
                count--;
            }

    };
    cdTimer = new Timer(500, action);
    cdTimer.start();
    match = true;
    count = countPassed;
}

//enable buttons other than btn and btn2
private void buttonEnable(JToggleButton btn, JToggleButton btn2){
    for(int i = 0; i < buttons.length; i++){
        if(buttons[i] != btn && buttons[i] != btn2)
            buttons[i].setEnabled(true);
    }
}

//disable buttons other than btn and btn2
private void buttonDisable(JToggleButton btn, JToggleButton btn2){
    for(int i = 0; i < buttons.length; i++){
        if(buttons[i] != btn && buttons[i] != btn2)
            buttons[i].setEnabled(false);
    }
}

private void unflipPair(JToggleButton btn, JToggleButton btn2){
    btn.setIcon(icon);
    btn2.setIcon(icon);
    btn.setEnabled(true);
    btn2.setEnabled(true);
    btn.setSelected(false);
    btn2.setSelected(false);
}

private void retirePair(JToggleButton btn, JToggleButton btn2){
    btn.setSelected(true);
    btn2.setSelected(true);
    btn.removeActionListener(this);
    btn2.removeActionListener(this);
    retireButton.add(btn);
    retireButton.add(btn2);
}

private void createIcons(){
    ImageIcon icon1 = new ImageIcon("1.png");
    ImageIcon icon2 = new ImageIcon("2.png");
    ImageIcon icon3 = new ImageIcon("3.png");
    ImageIcon icon4 = new ImageIcon("4.png");
    ImageIcon icon5 = new ImageIcon("5.png");
    ImageIcon icon6 = new ImageIcon("6.png");

    iconList.add(icon1);
    iconList.add(icon2);
    iconList.add(icon3);
    iconList.add(icon4);
    iconList.add(icon5);
    iconList.add(icon6);
}


public static void main(String args[]) {
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            if(args.length == 0) //java MemoryGame debug increases the string length to 1
                new MemoryGame();
            else
                new MemoryGame(2);
        }
    });
}

}

These are the addActionListener:

pause.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            elapsed += now;
            swTimer.stop();
        }
    });
resume.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            timerContinue();
        }
    });

This is timerContinue method:

public void continueTime(){
    long temp = Calendar.getInstance().getTimeInMillis();
    time.setText("Elapsed time is " + formatTime((long) (temp - start)));
}

private void timerContinue(){
    ActionListener timerAL = new ActionListener(){
        public void actionPerformed(ActionEvent e){
            continueTime();
        }
    };

    //stop the timer if it is still running
    if (swTimer != null && swTimer.isRunning()) {
        swTimer.stop();
    }

    swTimer = new Timer(1000, timerAL);
    swTimer.setInitialDelay(0);
    swTimer.start();
}

This is timeStart() method:

public void updateTime(){
    long temp = Calendar.getInstance().getTimeInMillis();
    time.setText("Elapsed time is " + formatTime((long) (temp - start)));
    now = temp - start;    
}

private void timerStart(){
    ActionListener timerAL = new ActionListener(){
        public void actionPerformed(ActionEvent e){
            updateTime();
        }
    };

    //stop the timer if it is still running
    if (swTimer != null && swTimer.isRunning()) {
        swTimer.stop();
    }

    swTimer = new Timer(1000, timerAL);
    swTimer.setInitialDelay(0);
    swTimer.start();
}

Answer 1

So, you capture start

private long start = Calendar.getInstance().getTimeInMillis();

when the class is first instantiated ... not sure this is a good idea, but lets flow with it...

When you pause the timer...

pause.addActionListener(new ActionListener(){
    public void actionPerformed(ActionEvent e){
        elapsed += now;
        swTimer.stop();
    }
});

you capture the elapsed time

When you resume the clock...

public void continueTime(){
    long temp = Calendar.getInstance().getTimeInMillis();
    time.setText("Elapsed time is " + formatTime((long) (temp - start)));
}

private void timerContinue(){
    ActionListener timerAL = new ActionListener(){
        public void actionPerformed(ActionEvent e){
            continueTime();
        }
    };

    //stop the timer if it is still running
    if (swTimer != null && swTimer.isRunning()) {
        swTimer.stop();
    }

    swTimer = new Timer(1000, timerAL);
    swTimer.setInitialDelay(0);
    swTimer.start();
}

You're using the current time and subtracting start , but start has never been reset, so it's still calculating from the time it was first initialised.

Conceptually, a "pause-able" clock is one which has two important states.

• The "current" run time. That is the time from when it was started/resumed to now
• The "previous" run time. That is the total amount of time that the timer has been allowed to run.

So. When you pause the clock, you need to do a couple of things...

1. Calculate the total running time for this phase - the time from when it was started to now.
2. Add that to an overall "running time", which keeps track of the total time the clock has been allowed to run.
3. Reset the start time (preferably to something like null , so it's obvious)

When resumed, you need to...

1. Store the current time, as the start time.
2. Calculate the time between the start time and now (when the clock ticks)
3. Add the totalRunningTime to it, which creates the overall running time for the clock.

Simple 😁

Firstly, the question itself is not that uncommon, and a number solutions are available if you spend some time researching the problem.

Having said that, since it's now 2018 and Java 11 is visible on the horizon, you really should be making use of Java's newer date/time API, which provides a number of really useful APIs, including Duration and the ability to treat time independently of the underlying calendar system ... so we don't get daylight savings oddities 😝

The following is an example of some library code I use, which implements the functionality from above.

The "strange" thing about it is, it's independent of a timing system. That is, it doesn't "tick". Instead, you'd use a Swing Timer (in your case) to call getDuration and update the UI as required.

public class StopWatch {

    private Instant startTime;
    private Duration totalRunTime = Duration.ZERO;

    public StopWatch start() {
        startTime = Instant.now();
        return this;
    }

    public StopWatch stop() {
        Duration runTime = Duration.between(startTime, Instant.now());
        totalRunTime = totalRunTime.plus(runTime);
        startTime = null;
        return this;
    }

    public StopWatch pause() {
        return stop();
    }

    public StopWatch resume() {
        return start();
    }

    public StopWatch reset() {
        stop();
        totalRunTime = Duration.ZERO;
        return this;
    }

    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;
    }
}

And if you want to see the concept in action, you could have a look at Adding resume function to stopwatch