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Which one is recommended and to be used to check the Object null-ness?
null != Object
or
Object != null
and other way
null == Object
or
Object == null
…and is there any difference between them?
(In)equality is commutative, so there is no difference.
Historically the former stems from C to avoid accidentally assigning a value in a conditional statement, however that mostly applies to
==, not!=. Also Java requires the condition in a conditional statement to have a boolean value, so the only place where it could go wrong nowadays would beif you accidentally omit one of the
=. A rare case, I guess (though probably not so much, given what students frequently write in their first two terms). Joonas also points out another (more obscure) case in the comments.