Transient vs Volatile modifiers in Java

By: Reema sen Printer Friendly Format

Java defines two interesting type modifiers: transient and volatile. These modifiers are used to handle somewhat specialized situations.

When an instance variable is declared as transient, then its value need not persist when an object is stored. For example:

class T {

transient int a; // will not persist

int b; // will persist

}

Here, if an object of type T is written to a persistent storage area, the contents of a would not be saved, but the contents of b would. The volatile modifier tells the compiler that the variable modified by volatile can be changed unexpectedly by other parts of your program. One of these situations involves multithreaded programs. In a multithreaded program, sometimes, two or more threads share the same instance variable. For efficiency considerations, each thread can keep its own, private copy of such a shared variable. The real (or master) copy of the variable is updated at various times, such as when a synchronized method is entered. While this approach works fine, it may be inefficient at times. In some cases, all that really matters is that the master copy of a variable always reflects its current state. To ensure this, simply specify the variable as volatile, which tells the compiler that it must always use the master copy of a volatile variable (or, at least, always keep any private copies up to date with the master copy, and vice versa). Also, accesses to the master variable must be executed in the precise order in which they are executed on any private copy.

Note: volatile in Java has, more or less, the same meaning that it has in C/C++.

This is an extract from the book 'Java Complete Reference'. For more details please refer to the book

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1. I think this clarification is not sufficient..If y
View Tutorial By: Abhinav at 2009-02-10 12:35:56

2. Your explanation is good and okay but, it will be
View Tutorial By: Emmanuel at 2009-05-28 02:45:11

3. Your explanation is perfectly clear and not in nee
View Tutorial By: Percy at 2009-06-08 14:14:39

4. Hi thanks for your information.

I g
View Tutorial By: karthikeyan at 2009-09-18 04:50:37

5. Your complete answer is taken from Herbert Schildt
View Tutorial By: Priyanka at 2009-10-31 07:29:05

6. Hello,

A volatile variable does not
View Tutorial By: aayush at 2009-11-16 07:38:23

7. If you are working with the multi-threaded program
View Tutorial By: Prithvi at 2010-01-07 10:24:12

8. You should consider using different threads that a
View Tutorial By: Jeremy at 2010-01-13 23:02:11

9. If you are working with the multi-threaded program
View Tutorial By: it career at 2010-02-24 00:13:50

10. Your explanation is good but, it will be better i
View Tutorial By: Jabaraj at 2010-03-22 06:02:33

11. This is an excerpt from Java Complete Reference.Ju
View Tutorial By: Guest at 2010-03-25 01:36:57

12. Explanation is very good. Thanks all.
View Tutorial By: reddy at 2010-04-07 08:47:09

13. The example is wrong, because there are two sepera
View Tutorial By: billGates at 2010-07-06 16:56:13

14. This example is working fine....I think BillGates
View Tutorial By: Monoj Rath at 2010-07-15 01:27:51

15. HI your explanation is absolutely correct but I am
View Tutorial By: Anil R. Chinchawade at 2010-07-28 02:02:01

16. Hi ,learn a new thing about These Transient and Vo
View Tutorial By: LakshmiNarayana Golla at 2010-07-28 02:49:48

17. Can some body throw more light on TRANSIENT ....
View Tutorial By: Anish at 2010-08-03 07:30:58

18. Very good explaination of transient and volatile.
View Tutorial By: Himanshu Upadhyay at 2010-11-15 04:48:43

19. What is transient keyword in Java?

View Tutorial By: Mohit at 2010-11-18 00:26:24

20. Real Life example of using Volatile
*******
View Tutorial By: Mayank at 2011-01-25 15:44:21

21. Nice artielce , by the way just to add from my exp
View Tutorial By: Javin @ eclipse remote debugging at 2011-03-11 22:00:15

22. Thanks Mohit ..... Clear Explanation abt Transien
View Tutorial By: Dhi at 2011-08-22 06:28:06

23. Hi there, I fixed the above (non-working) example
View Tutorial By: JavaBoy at 2011-09-24 05:41:19

24. i thnk exampleThread example is wrong - like billg
View Tutorial By: oldman at 2011-09-24 12:32:33

25. Transient: The transient modifier applies to varia
View Tutorial By: Manoj Yadav at 2011-11-23 09:33:23

26. There was no sharing of volatile variable in the p
View Tutorial By: Rajesh Poppoppu at 2011-12-30 13:04:42

27. Awesome, now I can say I've fully understood volat
View Tutorial By: Andrew at 2012-01-13 18:19:15

28. Straight tutorial, keep on working. Thanks
View Tutorial By: Gerson at 2012-04-09 19:42:19

29. This is not your explanation. This is from the boo
View Tutorial By: Subhaprasad Mukherjee at 2012-04-14 03:35:29

30. Copy and pasted from Java:The Complete Reference.
View Tutorial By: Imon at 2012-08-07 07:02:14

31. Hi, You explanation is good.
But it may be
View Tutorial By: Dishant at 2012-10-18 05:07:51

32. I think 19 floor's code doesn't fix the problem.Al
View Tutorial By: Benson at 2012-11-28 08:04:26

33. @Reema Sen:
It would have been better if yo
View Tutorial By: Mragank Singhal at 2013-02-13 04:37:06

34. it is really best site for the information.many ti
View Tutorial By: panchanan ruata at 2013-05-22 09:36:37

35. Updated example to better show Thread T2 showing t
View Tutorial By: Sanjiv at 2013-05-25 20:26:31

36. Tomorrow is my java's exam...ANd this is definitel
View Tutorial By: hardeep at 2013-05-28 08:51:55

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