What does CAS mean in Java?

In Java, CAS stands for Compare and Swap and is also known as a lock-free algorithm. It is a multi-threaded synchronization mechanism used to address data race conditions in concurrent environments.

CAS involves three parameters: the memory location (V), the expected value (A), and the new value (B). CAS will compare the current value at the memory location with the expected value, and if they are equal, it will update the value at the memory location to the new value; otherwise, it will not do anything. The entire comparison and update process is atomic.

CAS operations do not require traditional locking mechanisms to ensure thread safety, therefore it can effectively reduce the time that threads wait and improve concurrent performance. It is commonly used to implement lock-free data structures, atomic operations, etc. Examples include classes like AtomicInteger and AtomicLong in Java.