When is it preferable to use a synchronized method, and when a code block to ensure thread safety?

In Java, a synchronized method (synchronized method) locks the entire method for one thread, which is convenient when you need to protect all operations within the method from concurrent access.

Using a synchronized method is preferable when:

• The entire logic of the method must be executed atomically.
• The method is small and does not contain long operations, so as not to block the thread for a long time.

A code block with synchronized (synchronized block) is preferable when:

• You need to synchronize only part of the method, not the entire method.
• There is an opportunity to reduce the scope of locking, increasing parallelism.
• Synchronization is needed on a specific object, not on the current instance.

Example:

public void addItem(Item item) {
    // Non-critical part
    prepareItem(item);
    
    synchronized(this) {
        // Critical section
        items.add(item);
    }
}

Thus, the choice depends on how much of the code needs to be protected and how important performance is.