What is the role of the `synchronized` keyword in Java?

• A. To allow multiple threads to access a block of code
• B. To ensure only one thread can access a block or method at a time
• C. To create a monitor for concurrent execution
• D. To handle exceptions in multi-threaded applications

Answer: (B)

The synchronized keyword in Java is essential for controlling access to a shared resource when multiple threads are involved. Its primary role is to ensure that only one thread can access a block of code or a method at a time. This is crucial in a multi-threaded environment to prevent data inconsistency and to avoid race conditions, where two or more threads attempt to modify the same data simultaneously, potentially leading to unpredictable results.

When a thread enters a synchronized block or method, it acquires a lock (or monitor) associated with the object or class. Other threads that attempt to enter any synchronized block or method that shares the same lock will be blocked until the lock is released by the thread currently holding it. This mechanism guarantees that only the thread that has acquired the lock can execute the synchronized code, maintaining the integrity of the data being accessed.

While the other options mention relevant concepts related to threads, they do not accurately describe the specific function of the synchronized keyword. The first option misrepresents the keyword's function by suggesting multiple threads can simultaneously access synchronized code, which contradicts the fundamental purpose of synchronization. The third option refers to monitors, which while related to synchronization, does not directly explain the keyword's use in providing mutual exclusion