Explain synchronized block vs. method locking.

[sakshisukla]

In Java, synchronized block and synchronized method are both mechanisms to handle thread synchronization, ensuring that only one thread can access a critical section of code at a time. However, they differ in scope and flexibility.

Synchronized Method​

A synchronized method locks the entire method for the object (or class, if it's static). When a thread invokes a synchronized method, it obtains a lock on the object (or class-level lock if static) before entering the method. No other thread can execute any other synchronized method on that object until the first thread releases the lock.

Example:


public synchronized void increment() {
count++;
}

This method locks the whole method, even if only one line needs synchronization.

Synchronized Block​

A synchronized block, on the other hand, allows locking only a specific section of code within a method. This provides finer-grained control and can lead to better performance by reducing the time the lock is held.
Example:


public void increment() {
synchronized(this) {
count++;
}
}


Or, lock on a different object:


synchronized(lockObject) {
// critical section
}

Key Differences​

• Granularity: Synchronized block allows partial method locking; method locking applies to the whole method.
• Flexibility: Blocks can lock on any object, methods lock on this or class object.
• Performance: Blocks can improve performance by reducing lock contention.

In a multi-threaded Java application, using synchronized blocks effectively can lead to more scalable and responsive programs.
To learn synchronization and other concurrency techniques in detail, consider enrolling in a Java Full Stack Developer Course that covers core Java, advanced topics, and backend multithreading principles.