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Prime 24 Java Date, Time, and Calendar Interview Questions Solutions

The Date and Time API is a big one for day-to-day Java improvement work, however many interviewers do not ask sufficient questions on this matter. A lot of the questions are primarily based on both Java Assortment framework like  HashMap, ConcurrentHashMap, or ArrayList or multi-threading ideas like risky, synchronized, and atomic variables. This isn’t good, and plenty of interviewers have realized {that a} good understanding of date and time API can also be vital for a great Java developer. That is the principle motive for rising date, time, and calendar-based Java interview questions in latest occasions, notably within the final couple of years.

For the reason that Java improvement job market is ideal at this second. There are numerous jobs open, notably within the funding banking area within the Asia Pacific, its in all probability the very best time to alter your job, particularly if you’re caught with no studying, no wage increment and never a big bonus or incentives in final a few years.

Other than stability, development is important as a result of in the event you do not transfer ahead, you can be caught and ultimately transfer backward; therefore, altering a job is as vital as sticking to a working job.

If you’re new to Java and do not know a lot about Date and Time lessons, then I counsel you first undergo these Java Programming and Improvement programs. It is also not too long ago up to date to cowl the most recent Java model and isn’t very costly. You may get it in simply $10 in a number of Udemy flash gross sales, which occurs throughout the yr.

Prime 24 Date, Time, and Calendar Interview Questions and Solutions

I’ve been sharing interview questions on numerous Java matters from the final couple of years like multithreading, collections, design patterns, coding issues, and so on.. Nonetheless, one matter I have not touched but was date and time, and that is why I assumed to share among the fascinating Date and time-based questions from latest Java interviews. On this article, you’ll find these.

1. Does SimpleDateFormat be protected to make use of within the multithreaded program? (reply) 

Sadly, DateFormat and all its implementations, together with SimpleDateFormat, aren’t thread-safe; therefore, it shouldn’t be used within the multi-threaded program till exterior thread-safety measures are utilized e.g. confining SimpleDateFormat object right into a ThreadLocal variable. I

f you do not try this, you’re going to get an incorrect consequence whereas parsing or formatting dates in Java. Although, for all sensible date-time functions, I extremely suggest the joda-time library.

25 Java Date, Time, and Calendar Interview Questions Answers
2. How do you format a date in Java? like within the ddMMyyyy format? (reply
You may both use the SimpleDateFormat class or the joda-time library to format the date in Java. DateFormat class lets you format date on many standard codecs. Please see the reply for code samples to format the Date into totally different codecs like dd-MM-yyyy or ddMMyyyy.

3. Are you able to inform some variations between the previous and new Date Time API of Java 8? 

Although the brand new Date and Time API are a totally new APIs, you possibly can deduce the next distinction between them:

  • 1) Within the previous API, Date was mutable, however in Java 8, all date and time lessons like LocalDate, LocalTime, or LocalDateTime are Immutable.
  • 2) Within the previous API, SimpleDateFormat was not thread-safe, however in Java 8, Formatter is thread-safe.
  • 3) Within the previous Date and Calendar API, the 12 months begins with 1900, Months begin with 0, which is corrected in Java 8; right here, the numbers make extra sense.
  • 4) Outdated Date and Calendar API has only one class Date to symbolize date and time, however Java 8 has separated lessons for Date and Time e.g. LocalDate and LocalTime

4. Which date does the next Date occasion symbolize? 

Date aDate = new Date(2015, 12, 25, 20, 40);

It is a tough query for informal Java builders who haven’t any written date and time-based code as a result of this is not going to symbolize Christmas day or twenty fifth December 2015. This code has bought two bugs. First, the yr begins from 1900 to symbolize 2015, you’ll want to cross 115 i.e. 2015-1900.

The second situation with this code is that the month will not be right. The month begins from 0, so December could be 11, not 12, fascinating proper? That is why you need to new Date and Time API from Java 8, which solves all these points. Once more, you possibly can verify The Full Java Masterclass to study extra concerning the new Date and Time API.

Top 10 Java Date, Time and Calendar Interview Questions Answers

5. How do you copy a Date in Java? (reply) 

It is a easy query to reply. The Date class implements the clone() technique, so simply name the date.clone() to create a replica of the Date object in Java.

6. What’s the relationship between java.sql.Date and java.util.Date? (reply) 

This is likely one of the thrilling questions as not many builders know this nice however apparent element. The java.sql.Date extends java.util.Date and suppress all time-related strategies to behave as only a date class. That is in direct violation of the Liskov substitution precept.

7. Are you able to format Calendar in Java? (reply) 

No, the Calendar can’t be formatted in Java. You may solely format dates.

8. How do you change a Calendar to Date and vice-versa? (reply)

Properly, you should use the Calendar.setTime() and Calendar.getTime() technique to transform the Calendar to Date and vice-versa.

9. What’s the equal of Date class in Java 8? (reply)

The Occasion class is the equal to java.util.Date in Java 8 as a result of it additionally represents a millisecond worth or an occasion within the timescale. Java 8 has additionally added conversion technique e.g. toInstant() and fromDate() to transform occasion to java.util.Date and vice-versa. See Java SE 8 for Actually Impatient By Cay S. Horstmann for extra particulars.

Top 10 Java Date, Time and Calendar Interview Questions Answers

10. How do you change a millisecond to a Date in Java? (reply) 

One of many easiest inquiries to reply is the getTime() technique, which returns the millisecond from the Epoch.

12. How do you get a month and yr from a Date object in Java? (reply) 

You may convert a Date to a Calendar after which use its get() technique with numerous fields to get the month, yr, day of the week, and different date particulars e.g.

int day = calendar.get(Calendar.DATE); 
int month = calendar.get(Calendar.MONTH) + 1; 
int yr = calendar.get(Calendar.YEAR) + 1900; 

13. How do you change XMLGregorianCalendar to Date in Java? (reply)

I’ve mentioned this downside earlier than; please verify the hyperlink for an in depth reply.

14. How do you get the present time in GMT in Java? (reply)
The Java date is impartial of time and shows time in a present time zone provided that you print them. So, to transform the present time in GMT, you’ll want to use a Calendar with a time zone as proven within the given reply.

15. Is the Date class be Immutable in Java? (reply

No, the Date will not be immutable. You may change its inner to symbolize a distinct date. For this reason when you’ve got a member symbolize Date, you should be cautious to not leak its reference outdoors utilizing the getDate() technique as a result of then the shopper can modify the state of the Immutable object. As a substitute, a replica must be returned to the shopper as recommended within the Efficient Java e-book by none apart from Joshua Bloch, creator of a number of key lessons of JDK API.

Java Date, Time and Calendar Interview Questions Answers

16. How do you add and subtract a day, month, and yr in a Date object? (reply) 

This is likely one of the widespread day-to-day duties of a Java developer; you should use the code shared within the reply for including or subtracting a day or month from the Date object.

17. How do you examine two dates in Java to verify if they’re equal? (reply) 

This is likely one of the simpler questions you will notice when it comes to talent checking on Date lessons. The java.util.Date class implements the equals() technique, which returns true if each Dates are the identical and false in any other case.

18. How do you discover if one date comes earlier than or after one other date in Java? (reply) 
That is the follow-up query to the earlier query. The interviewer additional checks the candidate’s date comparability talent by asking this query. The reply is straightforward, the java.util.Date class supplies earlier than() and after() technique, which returns true and false if the date on which technique is known as comes earlier than or after the opposite date handed as a way argument.

19. How do you change java.util.Date to java.sql.Date in Java JDBC? (reply) 

It is the follow-up query of the sixth query. Since java.sql.The date is a subclass of java.util.Date you possibly can merely get the time in a millisecond and handed it to SQL date as proven beneath:

Date now = new Date();
java.sql.Date sqlDate = new java.sql.Date(now.getTime());

Easy and straightforward, proper? however there are some fascinating follow-up questions if you write this code; I counsel you verify the reply hyperlink for extra detailed dialogue, the place I’ve answered these follow-up questions as nicely. You may additional see Java Fundamentals: The Java Language to study extra about Java elementary ideas.

Java Date and Calendar Interview Questions Answers

20. The right way to convert native time to GMT in Java? (reply) 

That is much like one of many earlier questions the place we have to get the present time in GMT

21. How do you present timezone in formatted dates in Java? (reply)

see the reply hyperlink for a code instance

22. What’s the distinction between java.util.Date and java.sql.Date in Java? (reply) 

There may be a lot distinction between them, however a very powerful one is that java.sql.The date is from the JDBC package deal, and it acts as transformed between Date and Time information varieties within the database and Date in Java.

23. How do you calculate the distinction between two dates in Java? (program) 

There are a number of methods to calculate the distinction between two dates in Java e.g. you will get the lengthy millisecond values from two dates and get the distinction, however that is not very priceless; you principally want the distinction in days or hours. See this system to study extra about these variations.

24. How do you change a string (YYYYMMDD) so far in Java? (reply) 

You need to use SimpleDateFormat earlier than JDK 8 and DateTimeFormatter together with the format and parse technique to transform a string so far in Java.

That is all concerning the date, time, and Calendar primarily based Java Interview Questions. A Java developer must have a stable understanding of Java’s Date and Time API, each previous and new, as a result of you’ll not discover Java 8 in each challenge you’re employed on. You continue to have to know find out how to work with previous Date and Calendar API whereas sustaining the legacy challenge for a few extra years.

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Thanks for studying this text to this point. In case you like these questions, then please share them with your mates and colleagues too. When you’ve got any questions or suggestions, then please drop a notice.

P. S. – If you’re seeking to fill gaps in your Java data or wish to study Java from scratch, listed here are some helpful free on-line Java programs to take a look at at your comfort; they’re good for on-line studying out of your workplace or residence.



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