Group 1: Identifying characteristics

1 The adjective and noun have the same form adjective: the Japanese language noun: Nakamurasan is (a) Japanese

2 There is no difference between singular and plural ad]ectives/nouns singular: Nakamurasan is Japanese plural: Nakamurasan and Sanseidosan are Japanese

3 When referring to 'all the people, the is always required The Japanese are very clever people
country adjective countable noun plural or collective noun

Japan Japanese a Japanese (man/woman), the Japanese

two Japanese (men) Similarly e g Burma/Burmese, China/Chinese, Lebanon/Lebanese, Malta/Maltese, Portugal/Portuguese, Sudan/Sudanese, Surinam/Surinamese, Taiwan/Taiwanese, Switzerland/Swiss

Group 2: Identifying characteristics

1 The adjective and singular noun have exactly the same form
adjective: an Italian car noun: Mario is (an) Italian.

2 The plural noun adds -s the is optional in the plural (The) Italians are very creative [> 3.19.2]
country adjective countable noun plural or collective noun

Italy Italian an Italian (man/woman), two Italians (men) (the) Italians

Similarly e g

a) -ian endings add -n to countries ending in -ia Algena(n), Asia(n), Australia(n), Austna(n), Colombia(n), Indonesia(n), Nigena(n), Russia(n), Scandinavian), Syna(n), Tanzamafn), Tumsia(n) other -ian endings Argentina/Argentinian, Belgium/Belgian, Brazil/Brazilian, Canada/Canadian, Egypt/Egyptian, Hungary/Hungarian, Iran/Iranian, Jordan/Jordanian, Norway/Norwegian

b) generally add -n or -an Afnca(n), Amenca(n), Chile(an), Costa Rica(n), Cuba(n), Korea(n), Latin Amenca(n), Libya(n), Mexico/Mexican, Paraguayan), Uganda(n), Venezuela(n), Zimbabwe(an)

c) other endings CyprusZCypnot, Germany/German, Greece/Greek, Iraq/Iraqi, Kuwait/Kuwaiti, Oman/ Omani, Pakistan/Pakistani, Qatar/Oatan, Saudi Arabia/Saudi/Saudi Arabian, Thailand/Thai