When a race begins, the Start button is clicked . The message displayed at the top of the lap timer window changes from Stopped to Timing... and the lap counter and all the time displays are zeroed. As the runner finishes each lap, the Next lap button is clicked. This causes the lap counter to increase by 1 and the time and average speed displays to be updated. When the runner finishes the last lap, the Stop button is clicked and the timer is Stopped. Clicking the Stop button again has no effect until the timer has been restarted (at the beginning of the next race).

1. There's a problem with changing the lap length. Correct this problem 2. Another problem is that clicking the Stop button two or more times in a row causes the display to change repeatedly. Correct this problem. 3.Finally, several of the values displayed in the window are incorrect. Correct this problem.

public class TimingEngine { private boolean running; /* The number of laps that the runner has completed. */ private int lapCount; /* The time of the lap just completed, in milliseconds. */ private long lapTime; /* The total time the runner has run so far, in milliseconds. */ private long totalTime; /* The current time of the system clock when the runner * started the current lap, in milliseconds. * See getSystemTime(), at the end of this class. */ private long lapStartTime; /* The lap length, in metres. */ private int lapLength;

/* The average speed, in m/s. */ private int avgSpeed; /** * Create a TimingEngine object. The object will be initialised at 0, * status is "Stopped", ready to start timing. The default lap length * is 400 m. */ public TimingEngine() { running = false; lapCount = 0; totalTime = 0; lapTime = 0; avgSpeed = 0; lapLength = 400; }

/** * Instruct the timer to start timing a lap. * If we were not timing before, this starts the timer for a new * run. If we were already timing, this starts a new lap, adding the * current lap time to the total. */ public void startLap() { if (running) { finishLap(); } else { lapCount = 0; totalTime = 0; lapTime = 0; lapStartTime = getSystemTime(); running = true; } } /** * Stop timing. Add the current lap time to the total, and set * the timer into idle mode (waiting for a new run). */ public void stop() { finishLap(); running = false; } /** * Return the current status of the timer. The status is one of the * two Strings "Timing..." or "Stopped", indicating whether this * timer is currently running or stopped. */ public String getStatus() { if (running) { return "Timing..."; } else { return "Stopped"; } } /** * Return the number of laps completed in this run. */ public int getLapCount() { return lapCount; } /** * Return the time of the last lap completed. * The result is a string in the format "m:ss:hh", where m is * the number of minutes, ss the number of seconds, and hh the number * of hundredths of a second. For example "7:02:43". */ public String getLastTime() { return timeToString(lapTime); } /** * Return the average time for a lap in this run. * The result is a string in the format "m:ss:hh". */ public String getAverageTime() { if (lapCount == 0) { return timeToString(0); } else { long avgTime = totalTime / lapCount; return timeToString(avgTime); } } /** * Return the total time of the last or current run. * The result is a string in the format "m:ss:hh". */ public String getTotalTime() { return timeToString(totalTime); } /** * Return the average speed in this run in meters per second. * The result is a string such as "73 m/s". */ public String getAverageSpeed() { long totalSeconds = totalTime / 1000; if (totalSeconds == 0) { return "0 m/s"; } else { long avgSpeed = lapLength / totalSeconds; return avgSpeed + " m/s"; } } /** * Return the length of a lap. */ public int getLapLength() { return lapLength; } /** * Set the length of a lap. */ public void setLapLength(int length) { lapLength = length; }

/** * Private method called whenever a lap is finished. This method * updates the statistics. */ private void finishLap() { lapCount++; long lapEndTime = getSystemTime(); lapTime = lapEndTime - lapStartTime; totalTime = totalTime + lapTime; }

/** * Convert a time interval in milli-seconds into a String in the * format "m:ss:hh". */ private String timeToString(long time) { long hundredths = (time / 10) % 100; long seconds = (time / 1000) % 60; long minutes = time / 60000; return minutes + ":" + twoDigit(seconds) + ":" + twoDigit(hundredths); } /** * Convert a number into a two-digit String representation. */ private String twoDigit(long number) { if(number < 10) { return "0" + number; } else { return "" + number; } } /** * Return the current time of the system clock (in milli-seconds). */ private long getSystemTime() { return System.currentTimeMillis(); } }

public class LapTimer { private TimingEngine engine; private UserInterface gui; public LapTimer() { engine = new TimingEngine(); gui = new UserInterface(engine); } public void show() { gui.setVisible(true); } }