Synchronization

A synchronized method locks this for the entire method body, while a synchronized block locks a specific object for only the critical section, giving finer control and better concurrency.

Every Java object has an intrinsic monitor lock, and synchronized acquires it to provide mutual exclusion and memory visibility between threads.

Design thread-safe classes using four strategies in order of preference: immutability, confinement, delegation to thread-safe classes, and locking as a last resort.

Static synchronized locks on the Class object while instance synchronized locks on this, and because they are different locks, they can execute simultaneously.

Use per-account locks with synchronized blocks to protect concurrent balance operations, and acquire multiple account locks in consistent order to prevent deadlock during transfers.

Yes, the JVM automatically releases the monitor lock when an exception is thrown inside a synchronized block because the compiler generates two monitorexit instructions: one for normal exit and one for exceptional exit.

String literals are interned and shared across the entire JVM, so synchronizing on a String literal accidentally creates a global lock that blocks unrelated code.

Coarse-grained locking uses one lock for everything (simple but bottleneck), while fine-grained locking uses separate locks per resource (high concurrency but deadlock risk), and global lock ordering makes fine-grained safe.