Japanese vs Jap

Japanese and Jap both are nouns.

Word	Noun	Adjective	Verb	Adverb
Japanese	Yes	Yes	No	No
Jap	Yes	No	No	No

As nouns, Jap is a hyponym of Japanese; that is, Jap is a word with a more specific, narrower meaning than Japanese:

Other hyponyms of Japanese include Ryukyuan, Nip, geisha, geisha girl, shogun.

Japanese (noun)	Jap (noun)
the language (usually considered to be Altaic) spoken by the Japanese	(offensive slang) offensive term for a person of Japanese descent
a native or inhabitant of Japan

Japanese (adjective)	Jap (adjective)
of or relating to or characteristic of Japan or its people or their culture or language