What is volatile keyword in Java?

[Kajal]

What is volatile keyword in Java?

[Dfsindia]

It means, value of the variable cant be cached thread-locally.

[wordpar]

The volatile keyword could be used on every kind of variable, either primitive or objects.

[EdSim]

A volatile variable will instruct JVM threads to read value of volatile variable from main memory and don't cache it locally. If a variable is not shared between multiple threads no need to use volatile keyword with that variable.

[robert4u]

Volatile is applied to a variable when it is declared. It tells that value can change at any time.

[RH-Calvin]

Declaring a volatile Java variable means: The value of this variable will never be cached thread-locally: all reads and writes will go straight to "main memory"; Access to the variable acts as though it is enclosed in a synchronized block, synchronized on itself.

[aaidahnk]

volatile keyword in java- It changes the variable accross threads. The value of the variable will not be hiding the thread-locally, the data of all read and write threads will go directly into the main-memory, and it can be enclosed to adjust the access to the variable.

[JigsSamra]

Volatile?

"Volatile” tells the compiler that the value of a variable must never be cached as its value may change outside of the scope of the program itself.

[ab2345]

The value of this variable will never be cached thread-locally: all reads and writes will go straight to "main memory"; Access to the variable acts as though it is enclosed in a synchronized block, synchronized on itself.

[krupa]

Using volatile is yet another way (like synchronized, atomic wrapper) of making class thread safe. Thread safe means that a method or class instance can be used by multiple threads at the same time without any problem.

[damponting44]

The java volatile keyword guarantees that value of the volatile variable will always be read from main memory and not from thread's local cache.

[Ryan Harris]

1. volatile is the modifier applicable only for variables but not for methods and classes.
2. If the value of a variable kept on changing such type variables we have to declare with a volatile modifier.
3. If a variable declared as volatile then for every thread a separate local copy will be created.
4. Every intermediate modification performed by that thread will take place in a local copy instead of the master copy.
5. Once the value got finalized just before terminating the thread the master copy value will be updated with local stable value.
6. The main advantage of volatile keyword is we can resolve data inconsistency problems.
7. But the main disadvantage of volatile keyword is creating and maintaining a separate copy for every thread increases the complexity of the programming and effects performance of the system. Hence, if there is no specific requirement it is never recommend to use volatile keyword and it is almost outdated keyword.
8. volatile variable means it's value keep on changes where asfinal variable means its value never changes. Hence final volatile combination is illegal combination for variables.

[lengocdong]

Thanks

[Gaurav Joshi]

Using volatile is yet another way (like synchronized, atomic wrapper) of making class thread safe. Thread safe means that a method or class instance can be used by multiple threads at the same time without any problem.

[Akshay_M]

Volatile keyword is used in java synchronization technique to achieve thread safety,basically to overcome the visibility problem. The variables marked as volatile gets store in main memory rather than CPU cache.


Regards,
Akshay