如何通过 Java 中的参数传递方法引用？

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?

Answer 1

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))

Answer 2

You can use a simple lambda expression.

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

Answer 3

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); }