CODEWITHSUNDEEP
lambdajava-8interfacefunctional-interface
Payel Senapati
Payel Senapati

Reputation: 1356

In Function Interface declaration, how to pass another Function Interface as argument?

I want to do something like this -

final Function<Function<Integer, Integer>, Integer> function = (//appropriate syntax)

Is it possible to do so? If yes, what will be the correct syntax?

Upvotes: 0

Views: 47

Answers (2)

Payel Senapati
Payel Senapati

Reputation: 1356

The answer posted by Yassin Hajaj is perfect. However, I came up with an even better example for clearer understanding -

        final int base1 = 3;
        final int base2 = 5;
        final int index = 2;

        final Function<BiFunction<Integer, Integer, Integer >, Function<Integer, Integer>> power = func ->
                myIndex -> {
            int result = 1;
            int base = func.apply(base1, base2);
            for (int i = 1; i <= myIndex; i++) {
                result *= base;
            }
            return result;
        };

        final BiFunction<Integer, Integer, Integer> addition = (num1, num2) -> num1 + num2;

        final int result = power.apply(addition).apply(index);

        System.out.println("Result: " + result);

Output -

Result: 64

Here, there are two functions.

addition function's job is to define addition of two numbers.

power function takes addition function as argument, performs the addition of base1 and base2 to get the base. As a second argument power takes the index and then performs the power operation of base to the power index and returns the result.

Upvotes: 0

Yassin Hajaj
Yassin Hajaj

Reputation: 21975

Of course, it's totally possible, here is an example of how to implement it

int input = 2;
Function<Integer, Integer> times10Function = i -> i * 10;
Function<Function<Integer, Integer>, Integer> minus10Function = func -> func.apply(input) - 10;

Integer result = minus10Function.apply(times10Function);
System.out.println(result); // 10

The fact you can't do (i -> i + 10) -> ... is the same reason you can't use constants in methods signatures, these are placeholders, not actual implementations and they're thus piloted by the invoker

Upvotes: 2

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