What is true regarding the access of synchronized methods in Java?

• A. They can be accessed by multiple threads at the same time.
• B. A thread must acquire an object's lock to execute a synchronized method.
• C. Synchronized methods do not have locks associated with them.
• D. They can only be called by static methods.

Answer: (B)

In Java, synchronized methods are designed to control access to a block of code by multiple threads. When a method is declared as synchronized, it requires a thread to acquire the lock of the object that owns that method before executing it. This means that if one thread is executing a synchronized method on an object, other threads attempting to execute any synchronized method on the same object must wait until the lock is released.

This mechanism prevents concurrent access to the synchronized method, thereby avoiding issues like race conditions, where multiple threads may manipulate shared data simultaneously, leading to inconsistent or incorrect outcomes.

The other options do not accurately represent how synchronized methods function. For example, synchronized methods cannot be accessed simultaneously by multiple threads due to the locking mechanism in place, and synchronized methods do have locks associated with them. Finally, synchronized methods are not restricted to static methods; they can be instance methods as well. Thus, understanding the importance and mechanics of locks in synchronized methods is crucial for effective multithreaded programming in Java.