Count the arrows: Function is one in, one out. Supplier has no input, Consumer has no output.

Each functional interface is named after its shape. Function<T, R> takes a T and hands back an R, which may be a different type. Supplier takes nothing and produces something. Consumer takes something and returns nothing. Predicate takes something and answers true or false, and UnaryOperator is a Function whose input and output types must match.

Read it once, then a question tests whether the trick stuck.