Turn: differences between volatile and synchronized

Differences between volatile and synchronized:

1. volatile essentially tells the JVM that the value of the current variable in the register (Working Memory) is uncertain and needs to be read from the main memory. Synchronized locks the current variable, only the current thread can access this variable, and other threads are blocked.

2. Volatile can only be used at the variable level; synchronized can be used at the variable, method, and class level.

3. Volatile can only realize variable modification visibility and ensure atomicity. Synchronized can ensure variable modification visibility and atomicity.

4. Volatile will not cause thread blocking; synchronized may cause thread blocking.

5. Variables marked by volatile are not optimized by the compiler; variables marked by synchronized can be optimized by the compiler.