No, a null check is not needed before using instanceof.
x instanceof SomeClass is
From the Java Language Specification, section 15.20.2, "Type comparison operator instanceof":
"At run time, the result of the
trueif the value of the RelationalExpression is not
nulland the reference could be cast to the ReferenceType without raising a
ClassCastException. Otherwise the result is
So if the operand is null, the result is false.