As the JEP explains, the JVM has done both those things for a long time. In particular the object doesn't actually pay the price of a lock unless it's actually

As the JEP explains, the JVM has done both those things for a long time. In particular the object doesn't actually pay the price of a lock unless it's actually locked at some point. It used to be the case that the JVM was even more extreme and you wouldn't pay the price of a lock unless the object was actually contended, this was called biased locking, but the code complexity to implement it was eventually determined to be no longer worth it on modern hardware.