Do police officers swear an oath when they join the police force?

To become a member of the US military, a person swears an oath to uphold the Constitution. Do police officers swear something similar?

I’m curious, because the State of Hawaii Organization of Police Officers’ president recently testified during the hearings on the marriage equality bill that he would not enforce the marriage equality law. (article)

Let’s not discuss whether a law about marriage is enforceable or not.

I’m wondering whether police officers are sworn to enforce laws. If so, then the Honolulu Police Department’s response to the president’s testimony at the end of the article linked is important.