Method references with a parameter

Question

In Java 8, with the following class

 class Person {

    private boolean born;

    Person() {
    }

    public void setBornTrue() {
        born = true;
    }

    public void setBorn(boolean state) {
        born = state;
    }

  }

it is possible to call the setBornTrue method via a method reference:

    ArrayList<Person> people = new ArrayList<>();
    people.add(new Person());

    people.forEach(Person::setBornTrue);

but how would I use the forEach method and use the setBorn using a method reference? Trying:

    people.forEach(Person::setBorn);

results in an error, "Cannot resolve method setBorn".

In addition, how would I pass in the value of True?

What are you trying to achieve ? This is wrong - `people.add(new Person(null));people.forEach(Person::setBornTrue);` — Erran Morad, Aug 24 '14 at 05:14
`people.add(new Person(null));` is this line right ? why null ? your code works for me but if you removed `null`. — , Aug 24 '14 at 05:14
Take a look at MethodHandle, but it so complicated, nothing like std::bind in C++ — Martin Meeser, Jan 30 '20 at 09:58

Volune · Accepted Answer · 2014-08-24T05:46:44.087

27

With lambda:

people.forEach((p) -> p.setBorn(true));

Found no other ways only using the java 8 API.

With this custom function:

public static <T, U> Consumer<T> bind2(BiConsumer<? super T, U> c, U arg2) {
    return (arg1) -> c.accept(arg1, arg2);
}

You can do:

people.forEach(bind2(Person::setBorn, true));

If this kind of utility methods is available in the java API or in a library, please let us know.

edited Aug 24 '14 at 05:46

answered Aug 24 '14 at 05:18

Volune

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23

Yes ... while the answer above is how to set this *without* a method reference, is there no way to code this *with* a method reference? – Dakotah North Aug 24 '14 at 05:31
@user465342 Updated with an alternative solution, which is not plain java, but uses a method reference. – Volune Aug 24 '14 at 05:47
Very impressive! Is there any reference you used to create that? Been looking for a good resource. – Dakotah North Aug 24 '14 at 06:36

Method references with a parameter

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