Store constructor that accepts parameter in reference

Question

I have a class

public class Person {
    private int age;
}

And using Supplier in java 8 , I can store the constructor reference like

Supplier<Person> personSupplier = Person::new

But what if my constructor accepts parameter age like

public class Person {
    private int age;
    public Person(int age) {this.age = age;}
}

Now

Supplier<Person> personSupplier = Person::new

doesn't works, so what should be correct signature for the personSupplier? Obviously I can do something like.

Supplier<Person> personSupplier = () -> new Person(10);

But age must be different for each person, so it doesn't solve my problem.

May be I should use something else instead of Supplier?

Answer 1

You can use java.util.function.Function in Java and supply age when calling apply.

E.g.

Function<Integer, Person> personSupplier = Person::new;
Person p1 = personSupplier.apply(10);
Person p2 = personSupplier.apply(20);

Which is equivalent to

Function<Integer, Person> personSupplier = (age) -> new Person(age);
    Person p1 = personSupplier.apply(10);
    Person p2 = personSupplier.apply(20);

Answer 2

So what should be correct signature for the personSupplier?

That would be Function<Integer, Person> or IntFunction<Person>.

You can use it as follows:

IntFunction<Person> personSupplier = Person::new;

Person p = personSupplier.apply(10);  // Give 10 as age argument

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Follow-up:

What if I have Person(String name, int age)?

You could use BiFunction<String, Integer, Person> the same way as above.

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Follow-up #2:

What if I have Person(String firstName, String lastName, int age)?

You won't find a suitable type in the API. You'd have to create your own interface as follows:

@FunctionalInterface
interface PersonSupplier {
    Person supplyPerson(String firstName, String lastName, int age);
}

This could then be used the same way:

PersonSupplier personSupplier = Person::new;  // Assuming a Person has a name

Person p = personSupplier.supplyPerson("peter", "bo", 10);