According to JLS(§:9.1.3):
Given a generic interface declaration I<F1,...,Fn> (n > 0), the direct superinterfaces of the parameterized interface type I<T1,...,Tn>, where Ti (1 ≤ i ≤ n) is a type, are all types J<U1 θ,...,Uk θ>, where J<U1,...,Uk> is a direct superinterface of I<F1,...,Fn> and θ is the substitution [F1:=T1,...,Fn:=Tn].
What is the meaning of θ as here? Can this be explained with some example expression for how θ is the substitution [F1:=T1,...,Fn:=Tn] holds?