Passing function references as parameters

Question

Is it possible to pass a reference to a method as a parameter?

For example:

public static void main(String[] args) {
    String data = "name: John, random text, address: leetStreet";
    Person person;

    //if regex matches, use method reference, to send the result. 
    applyDataToPerson(data, "name: (\\w+)", person, Person::setName);
    applyDataToPerson(data, "address: (\\w+)", person, Person::setAddress);
}

private static void applyDataToPerson(String data, String regex, Person person, 
 Function<Person> f) {
    Matcher match = Pattern.compile(regex).matcher(data);
    if (match.matches()) person.f(match.group(1));
}

class Person {
    private String name;
    private String address;

    public void setName(String name) {
        this.name = name;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

If not, what would be an alternative to giving a reference to a method? Switch-case construct?

In Java 8 you can pass method references to existing methods (among other things) — Tibrogargan
– Tibrogargan, Commented Oct 27, 2016 at 21:44
@Tibrogargan how would the method signature look like? Comparator <? super T> does not make sense to me. — JasperJ
– JasperJ, Commented Oct 27, 2016 at 21:51
What is Function<Person> supposed to represent? If we're talking about java.util.function.Function, it has 2 generic types, not 1. So that code cannot compile to begin with... (let alone person.f(...)). Before asking for alternatives, make sure you have working code... — Tunaki
– Tunaki, Commented Oct 27, 2016 at 22:00

shmosel · Accepted Answer · 2016-10-27 22:00:28Z

5

I think you're looking for BiConsumer:

private static void applyDataToPerson(String data, String regex, Person person, BiConsumer<Person, String> action) {
    Matcher match = Pattern.compile(regex).matcher(data);
    if (match.matches()) action.accept(person, match.group(1));
}

Alternatively, you can shorten the method signature and use a single-argument Consumer that captures your person reference:

public static void main(String[] args) {
    String data = "name: John, random text, address: leetStreet";
    Person person;

    //if regex matches, use method reference, to send the result. 
    applyData(data, "name: (\\w+)", person::setName);
    applyData(data, "address: (\\w+)", person::setAddress);
}

private static void applyData(String data, String regex, Consumer<String> action) {
    Matcher match = Pattern.compile(regex).matcher(data);
    if (match.matches()) action.accept(match.group(1));
}

edited Oct 27, 2016 at 22:00

answered Oct 27, 2016 at 21:55

shmosel

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3 Comments

gaston Over a year ago

And in your main method write the biconsumer function :

applyDataToPerson(data, "name: (\\w+)", person, (Person p, String s) -> p.setName(s) );         applyDataToPerson(data, "address: (\\w+)", person, (Person p,String s) -> p.setAddress(s));

shmosel Over a year ago

@gaston No, the main method is exactly as OP had it.

xiaofeng.li Over a year ago

Personally I like the second option.

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