Albert Barnes Commentary 1 Kings 13:2

"And he cried against the altar by the word of Jehovah, and said, O altar, altar, thus saith Jehovah: Behold, a son shall be born unto the house of David, Josiah by name; and upon thee shall he sacrifice the priests of the high places that burn incense upon thee, and men`s bones shall they burn upon thee." — 1 Kings 13:2 (ASV)

A child shall be born ... Josiah by name - Divine predictions so seldom include such specific details that doubts are raised, even by orthodox theologians, regarding the actual mention of Josiah’s name by a prophet living in the time of Jeroboam. Only one other parallel instance occurs in all of Scripture: the mention of Cyrus by Isaiah. Of course, no one who believes in divine foreknowledge can doubt that God could, if He chose, cause events to be foretold in great detail by His prophets. However, it is a general principle of His providence that He does not do this. If this principle is to be broken, it will not be done arbitrarily.

In this case, it is not clear what great effect was produced by mentioning Josiah’s name so long before his birth, which raises the question of whether our present copies contain the true original text. The meaning is complete without the words “Josiah by name.” If these words were originally a marginal note, they could have easily crept into the text through a copyist's mistake. It is remarkable that in a later reference to this narrative in the book of Kings, there is no mention that the man of God had prophesied of Josiah “by name.”