The Java Volatile Keyword

Question 1

What is the Java Volatile Keyword used for?

Answer 1

It is used to guarantee visibility of changes to variables across threads

Question 2

What does it mean to declare a variable as Volatile to the JVM?

Answer 2

By declaring the a variable volatile, all writes to the variable will be written back to main memory immediately.
Also, all reads of the variable will be read directly from main memory.

Question 3

What does it mean to declare a variable as Synchronised to the JVM?

Answer 3

Synchronised basically adds a critical flag to a specific variable. Thus, the JVM will know to block all but one write request to the variable at a time. It will, however, allow infinitely many simultaneous read requests - as long as no write request is currently occurring.

Question 4

When should you use Volatile

Answer 4

Use Volatile when your variables are going to get read by multiple threads, but written to by only one thread.

Question 5

When should you use Synchronised?

Answer 5

Use Synchronised when your variables will get read and written to by multiple
threads