Keyword : volatile

[peiceonly]

What is this used for ?
Why this is not used for local variables

[goldhouse]

The volatile keyword is used on variables that may be modified simultaneously by other threads. This warns the compiler to fetch them fresh each time, rather than caching them in registers. This also inhibits certain optimisations that assume no other thread will change the values unexpectedly. Since other threads cannot see local variables, there is never any need to mark local variables volatile.

[cruxblack]

I haven't quite get the matter, could u give some examples bout the subject goldhouse?
Or maybe a link about it, kinda hard to understand it sometimes without an example

Thanks
CruxBlack

[jdev]

goldhouse example is a good one. I'll give you a different example.

Volatile comes from the C language (not sure C was the first to use it, though!). If you have a hardware register which represents a temperature value, for example, if you don't tell the compiler that that address is volatile the compiler might use an internal register to store that value, which would be wrong because the value keeps changing (in the external device) while the value in internal register won't change. In this case volatile means "get always the value from this address".
Hope this helps

[goldhouse]

thanks jdev

[cruxblack]

Err...i havent dig too much into threading and concurrency actually, have been reading about it from some books, but i still haven't understand much of its concept
All i can think when u say

Quote:

Originally Posted by jdev

"get always the value from this address"

was, doesn't the static keyword do the same thing? Though, i realize that may not be the case
Ill start a thread in the New to Java section since my questions are gonna be rather basic bout threading and unfit in the Advanced Java, but thanks all

CruxBlack

[vibhor.ec]

u cant' serialize volatile variables.i.e. cant save the volatile varible of an object