If a male masturbates before giving a urine test sample, can doctor detect that the man has masturbated?

Yes: But only if they specifically check for sperm.

Really, no: If the urine is mid-stream, you're unlikely to see sperms under the microscope. Plus, there's no way to know whether you masturbated, had a nocturnal emission, or had sex. Love responsibly, and if you need to, talk with somebody sensible. And especially -- enjoy being a man. Congratulations.