A synchronized block in Java is used to control access to a specific section of code by multiple threads, ensuring thread safety. It allows developers to synchronize only the critical part of the code rather than the entire method, improving performance. The block is enclosed using the synchronized keyword, followed by an object reference that acts as the monitor lock. Only one thread can execute the synchronized block on the same monitor object at a time, while others are blocked until the lock is released. For example:
This is useful for protecting shared resources like variables, files, or data structures.