What is the difference between synchronized and volunta…

synchronized and volatile are keywords in Java used for handling multi-threading programming, with the main difference being:

1. Different scope of application.

1. synchronized: used to modify a method or code block, ensuring that only one thread can access the modified method or code block at a time.
2. volatile is used to modify variables to ensure that multiple threads can correctly read and modify the modified variables.

1. The implementation mechanisms are different.

1. Synchronized: Achieving thread synchronization by obtaining an object’s lock, where other threads must wait if one thread already holds the lock.
2. Volatile: Ensures the visibility of variable values among multiple threads by using a special register barrier instruction in memory, requiring each variable access to read and write from main memory.

1. Different scenarios apply:

1. Synchronized: suitable for situations where atomic operations on shared resources or mutual exclusion access to code blocks are needed.
2. The “volatile” keyword is suitable for variables like flag or status indicators that need to be accessed and updated by multiple threads for simple state checks, without involving complex operations.

1. Different performance costs.

1. Synchronization may cause some performance overhead due to the need to acquire and release locks.
2. Volatile has lower performance overhead compared to synchronized because it does not involve acquiring and releasing locks.

In conclusion, synchronized is mainly used to achieve thread synchronization, while volatile is mainly used to ensure variable visibility. In different scenarios, choosing to use synchronized or volatile can better meet the needs of thread safety and performance.