1. Time is not on my side

2. Guess the Output – Part 1 try it: https://ideone.com/f9Qj4C
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); dateFormat.setTimeZone(TimeZone.getTimeZone("America/Chicago")); String dateString1 = " :50:00"; // May 26th 2017, 10:50:00 AM String dateString2 = " :50:01"; // May 26th 2017, 10:50:01 AM Date date1 = dateFormat.parse(dateString1); // Parse string to date Date date2 = dateFormat.parse(dateString2); // Parse string to date long milliSecondDifference = date2.getTime() - date1.getTime(); // Subtract dates long secondsDifference = milliSecondDifference / 1000; // Milliseconds to Seconds System.out.println(secondsDifference);
Correct output is 1 second
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3. Guess the Output – Part 2 try it: https://ideone.com/KZ9DXg
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); dateFormat.setTimeZone(TimeZone.getTimeZone("Asia/Shanghai")); String dateString1 = " :54:16"; // December 31st :54:16 PM String dateString2 = " :54:17"; // December 31st :54:17 PM Date date1 = dateFormat.parse(dateString1); // Parse string to date Date date2 = dateFormat.parse(dateString2); // Parse string to date long milliSecondDifference = date2.getTime() - date1.getTime(); // Subtract dates long secondsDifference = milliSecondDifference / 1000; // Milliseconds to Seconds System.out.println(secondsDifference);
Expected output is 1 second
Correct output is 344 second
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4. Why?
Backup link:
Start 18s
End 7:36

5. Stack Overflow - Question

6. Stack Overflow - Answer

7. 2012 Microsoft Azure Bug
Occurred at 4:00 PM on February 28th, 2012 (PST)
Code calculated a certificate expiration date, 1 year from the current issuing date.
February 29th, 2013 is not a valid date, caused a cascading failure
Caused service disruptions to Azure for 12 hours
SYSTEMTIME st; // declare a SYSTEMTIME variable
GetSystemTime(&st); // set it to the current date and time
st.wYear++; // increment it by one year
February 28th, 2012 (PST) is 00:00 February 29th (UST)

8. isLeapYear(int year) { return year % 4 == 0 }
Fixing the bug
isLeapYear(int year) { return year % 4 == 0 }
What about the year 2100 (not a leap year)
They skip centuries

9. Moral of the Story Don’t reinvent the wheel Know your edge cases
DateTime.AddYears will take into account leap years
Know your edge cases
Test your edge cases