How To Pass A Method Reference With Parameter In Java?

Question

I don't know the exact name for it (I'm guessing method-reference) but here is what I'm talking about. Let's say I want to take the square root of all doubles in a double array. Then, if the array is called arr, I can do this:

Arrays.stream(arr).map(Math::sqrt). // ... box it and stuff

However, if I want to square each number in an int array, I'm thinking of using Math.pow(num, 2) as the method. However, Math.pow has a second parameter, but I know it will always be 2. So I'm thinking I can do something like this:

Arrays.stream(arr).map(Math::pow(2)). // ... box it and stuff

But this results in an error. What can I do?

I think you have two ways: - Write a fun with 1 param (num), then return Math.pow(num, 2), use that fun for method reference. - just use it*it for the square on map function without method reference. — Phong Nguyen
– Phong Nguyen, Commented Jul 2, 2020 at 6:57
You can't use a method reference here, just use a lambda instead. .mapToDouble(n -> Math.pow(n, 2)) — Ravindra Ranwala
– Ravindra Ranwala, Commented Jul 2, 2020 at 6:59
Method reference only work if the method has the same input param + return type with the main method of target functional interface (geeksforgeeks.org/functional-interfaces-java) — Phong Nguyen
– Phong Nguyen, Commented Jul 2, 2020 at 7:01
I mean, if you use Math.pow(num, 2) directly it can't be referenced, if you write another method that have 1 param and return a double, that method can be referenced in this case, I'll show you the code if needed. — Phong Nguyen
– Phong Nguyen, Commented Jul 2, 2020 at 7:03
Or are you talking about partial application? (which, in this instance, would be overkill) — Federico klez Culloca
– Federico klez Culloca, Commented Jul 2, 2020 at 7:09

Amit Dony · Accepted Answer · 2020-07-02 07:00:15Z

3

you may use lambda and send Math.pow(n,2)

like this:

Stream.of(1.1,1.2,1.3).map(n -> Math.pow(n,2))

answered Jul 2, 2020 at 7:00

Amit Dony

312 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Higigig Over a year ago

Do you know how to pass in a method reference instead of using a lambda? I'm just wondering if it's possible, because I think it makes it look cleaner.

Holger Over a year ago

@Higigig no, it would not make the code cleaner. It would make it look different, that’s all.

Federico klez Culloca · Accepted Answer · 2020-07-02 07:02:27Z

1

You can use a simple lambda expression.

Arrays.stream(arr).map(d -> Math.pow(d, 2));

edited Jul 2, 2020 at 7:02

answered Jul 2, 2020 at 6:58

Federico klez Culloca

27.3k17 gold badges61 silver badges102 bronze badges

Comments

Phong Nguyen · Accepted Answer · 2020-07-02 08:13:03Z

0

There are 2 ways to implement this:

First, use lambda expression:

Arrays.stream(arr).map(num -> Math.pow(num, 2));

Second, (if you still want to invoke a method reference here, and to understand correctly how method reference works): write another method that call Math.pow():
```
Arrays.stream(arr).map(this::square);


private double square(double num) {
    return Math.pow(num, 2);
}
```

answered Jul 2, 2020 at 8:13

Phong Nguyen

7,1772 gold badges28 silver badges37 bronze badges

Collectives™ on Stack Overflow

How To Pass A Method Reference With Parameter In Java?

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related