What is the difference between a synchronized method and a synchronized block?

A synchronized instance method locks on the object instance (this) for the entire duration of the method call, while a synchronized static method locks on the Class object itself. A synchronized block, by contrast, lets you choose exactly which object to lock on and exactly which lines of code fall inside the critical section. Blocks are generally preferred over synchronizing whole methods because they give finer-grained control: the lock is held for less time (only around the code that actually needs protection), you can use a dedicated private lock object so external code can't accidentally interfere with your locking, and you can use multiple independent lock objects to protect different resources within the same class without unnecessarily serializing unrelated operations.