'Swore' in the Bible

All the people came to cause David to eat bread while it was yet day; but David swore, saying, "God do so to me, and more also, if I taste bread, or anything else, until the sun goes down."

The king said to Shimei, "You shall not die." The king swore to him.

But Abishai the son of Zeruiah helped him, and struck the Philistine, and killed him. Then the men of David swore to him, saying, "You shall go no more out with us to battle, that you don't quench the lamp of Israel."