Volatile variable

Generally speaking, the volatile keyword is intended to prevent the compiler from applying any optimizations on the code that assume values of variables cannot change "on their own."

The Java programming language also has the volatile keyword, but it is used for a somewhat different purpose. When applied to a field, the Java volatile guarantees that:

1. (In all versions of Java) There is a global ordering on the reads and writes to a volatile variable. This implies that every thread accessing a volatile field will read its current value before continuing, instead of (potentially) using a cached value. (However, there is no guarantee about the relative ordering of volatile reads and writes with regular reads and writes, meaning that it's generally not a useful threading construct.)
2. (In Java 5 or later) Volatile reads and writes establish a happens-before relationship, much like acquiring and releasing a mutex.^[8]

Using volatile may be faster than a lock, but it will not work in some situations.^{[citation needed]} The range of situations in which volatile is effective was expanded in Java 5; in particular, double-checked locking now works correctly.