There are more than one artist who use "J" as their name.
1. Jun Onose (Born on August 12, 1970 in Hadano, Kanagawa, Japan), referred to by his stage name J, is a Japanese musician, singer-songwriter and record producer. He is best known as bassist, co-founder and leader of the rock band Luna Sea. After the group disbanded in 2000 he focused on his solo career, for which he performs lead vocals and bass. He has recently rejoined Luna Sea as they reunited in August 2010.
2. J (real name Jani Savolainen is finnish musician who plays mainly guitar and is composing music. He is born in January, 8, 1982. He is also capable of playing bass.
He have played in Refrain named band. Nowdays Jani plays in band called Project Silence and Moukka.
3. J is pseudonym of solo artist from Czech Republic. He plays "solo garage folk". So far he released EP Bears (2010), EP Run from the Town (2011) and EP Cold Cold Nights (2012). Listen & download for free here http://bandzone.cz/j
4. J is a South African rock singer/songwriter who released his debut album, "Closure", in 2007.