“Hello”or “Hi” has no equivalent in Japanese. But there are words that can come close enough. Consider the basic Japanese greetings:
Ohayou gozaimasu – Good morning
Konnicha wa – Good day, good afternoon
Konban wa – Good evening
Oyasumi nasai – Good night
The usage of all the above is similar to their English equivalents. “Oyasumi nasai” is used at the end of a conversation. The other three are used in the beginning of a conversation and can double as a light “hello” too.
“Doumo” is another word that works like “hello”. It’s a little informal and is normally used with people you know quite well. “Doumo”with a slight bow roughly means “hello, how do you do”. The reply to this would be another “doumo”.
You would say “hajimemashite” if you are meeting someone for the the first time. It means “pleased to meet you”. If you are meeting someone after a long time, you would probably say “Ohisashiburi desu” which means “It’s been a while”.
Then there’s the super formal “Gokigenyo”, which means “hello, how do you” and “good bye, farewell”as well.
But, if you are a student in a Japanese university, you would probably just greet your friends with a cool “YO”!