Static variable is a class variable but not instance variable which is declared and initialized once in its life and shared by any number of instances.
Volatile keyword in Java is used as an indicator to Java compiler and Thread that do not cache value of this variable and always read it from main memory.
So if you want to share any variable in which read and write operation is atomic by implementation e.g. read and write in an int or a boolean variable then you can declare them as volatile variable.
So, declaring a static variable in Java, means that there will be only one copy, no matter how many objects of the class are created. The variable will be accessible even with no Objects created at all. However, threads may have locally cached values of it.
=> If its used in single thread environment, even if the copy of the variable will be updated and there will be no harm accessing it as there is only one thread.
=> Now if static variable is used in multi-threading environment then there will be issues if one expects desired result from it. As each thread has their own copy then any increment or decrement on static variable from one thread may not reflect in another thread.
https://stackoverflow.com/questions/2423622/volatile-vs-static-in-java
Here are few differences between volatile and synchronized keyword in Java.
1. The volatile keyword in Java is a field modifier while synchronized modifies code blocks and methods.
2. Synchronized obtains and releases the lock on monitor’s Java volatile keyword doesn't require that.
3. Threads in Java can be blocked for waiting for any monitor in case of synchronized, that is not the case with the volatile keyword in Java.
4. Synchronized method affects performance more than a volatile keyword in Java.
5. Since volatile keyword in Java only synchronizes the value of one variable between Thread memory and "main" memory while synchronized synchronizes the value of all variable between thread memory and "main" memory and locks and releases a monitor to boot. Due to this reason synchronized keyword in Java is likely to have more overhead than volatile.
6. You can not synchronize on the null object but your volatile variable in Java could be null.
7. From Java 5 writing into a volatile field has the same memory effect as a monitor release, and reading from a volatile field has the same memory effect as a monitor acquire
In short, volatile keyword in Java is not a replacement of synchronized block or method but in some situation is very handy and can save performance overhead which comes with use of synchronization in Java.
Volatile keyword in Java is used as an indicator to Java compiler and Thread that do not cache value of this variable and always read it from main memory.
So if you want to share any variable in which read and write operation is atomic by implementation e.g. read and write in an int or a boolean variable then you can declare them as volatile variable.
So, declaring a static variable in Java, means that there will be only one copy, no matter how many objects of the class are created. The variable will be accessible even with no Objects created at all. However, threads may have locally cached values of it.
=> If its used in single thread environment, even if the copy of the variable will be updated and there will be no harm accessing it as there is only one thread.
=> Now if static variable is used in multi-threading environment then there will be issues if one expects desired result from it. As each thread has their own copy then any increment or decrement on static variable from one thread may not reflect in another thread.
https://stackoverflow.com/questions/2423622/volatile-vs-static-in-java
Here are few differences between volatile and synchronized keyword in Java.
1. The volatile keyword in Java is a field modifier while synchronized modifies code blocks and methods.
2. Synchronized obtains and releases the lock on monitor’s Java volatile keyword doesn't require that.
3. Threads in Java can be blocked for waiting for any monitor in case of synchronized, that is not the case with the volatile keyword in Java.
4. Synchronized method affects performance more than a volatile keyword in Java.
5. Since volatile keyword in Java only synchronizes the value of one variable between Thread memory and "main" memory while synchronized synchronizes the value of all variable between thread memory and "main" memory and locks and releases a monitor to boot. Due to this reason synchronized keyword in Java is likely to have more overhead than volatile.
6. You can not synchronize on the null object but your volatile variable in Java could be null.
7. From Java 5 writing into a volatile field has the same memory effect as a monitor release, and reading from a volatile field has the same memory effect as a monitor acquire
In short, volatile keyword in Java is not a replacement of synchronized block or method but in some situation is very handy and can save performance overhead which comes with use of synchronization in Java.
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