How to use static constructor reference with a three parameters Java 8 Function (without make TriFunction)? - java-8

Question

I am currently playing with Java 8 and I found a problem with Function. I would like ton know if there is a way to use function reference (name::methode) with a Function with tree parameters without declare a new functional interface (i.e. TriFunction).
I tried with currying way, but it doesn't work.
I have three classes :
Person.class
public class Person {
public enum Sex {
MALE, FEMALE
}
private String firstName;
private String lastName;
private Sex gender;
public Person(String firstName, String lastName, Sex gender) {
this.firstName = firstName;
this.lastName = lastName;
this.gender = gender;
}
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
public Sex getGender() {
return gender;
}
}
PersonFactory
public class PersonFactory {
public static Person create(String firstName, String lastName, String gender) {
// Check firstName Parameter
if(firstName == null || firstName.isEmpty()) {
throw new IllegalArgumentException("The firstName argument expect to not be null or empty");
}
// Check lastName Parameter
if(lastName == null || lastName.isEmpty()) {
throw new IllegalArgumentException("The lastName argument expect to not be null or empty");
}
// Check gender Parameter
if(gender == null || gender.isEmpty()) {
throw new IllegalArgumentException("The gender argument expect to not be null or empty");
} else {
switch(gender) {
case "M":
return new Person(firstName, lastName, Sex.MALE);
case "F":
return new Person(firstName, lastName, Sex.FEMALE);
default:
throw new IllegalArgumentException("The gender parameter is supposed to be either 'M' for male or 'F' for Female");
}
}
}
}
CsVPersonParser
public class CsvPersonParser {
public Person parseLine(String line, String separator, Function<String, Function<String, Function<String, Person>>> creator) {
String[] separedLine = line.split(separator);
String firstName = separedLine[0];
String lastName = separedLine[1];
String gender = separedLine[2];
return creator.apply(firstName).apply(lastName).apply(gender);
}
}
Here is my main class :
public class App {
public static void main(String[] args) {
final String IMAGINARY_CSV_FILE_LINE = "Jean,Dupont,M";
CsvPersonParser csvParser = new CsvPersonParser();
csvParser.parseLine("blabla", ",", PersonFactory::create);
}
}
The compilator show : The type PersonFactory does not define create(String) that is applicable here
It seems pretty logical. I have no solution. Is anyone can help me ?

Answer 1

I wonder why there is no way to do it simple without to create new things.
Probably a tri function is quite complex. I suggest that you use a builder to create a person.
The main reasons are, that you are not fixed on parameter ordering and you can extend your person. When you use a trifunction where all parameters are strings its often hard to say which parameter is the first/second/third. And when you want to add an address to a person it becomes more difficult to make it with generic classes like TriFunction.
My suggestion:
public interface PersonBuilder {
PersonBuilder withFirstName(String firstName);
PersonBuilder withLastName(String lastName);
PersonBuilder withGender(String gender);
Person create();
}
Concrete Implementation:
public class DefaultPersonBuilder implements PersonBuilder {
private String firstName;
private String lastName;
private String gender;
#Override
public PersonBuilder withFirstName(String firstName) {
this.firstName = firstName;
return this;
}
#Override
public PersonBuilder withLastName(String lastName) {
this.lastName = lastName;
return this;
}
#Override
public PersonBuilder withGender(String gender) {
this.gender = gender;
return this;
}
#Override
public Person create() {
// Check firstName Parameter
if (firstName == null || firstName.isEmpty()) {
throw new IllegalArgumentException("The firstName argument expect to not be null or empty");
}
[... your implementation using the fields]
}
}
Your parser method:
public Person parseLine(String line, String separator, PersonBuilder person) {
String[] separedLine = line.split(separator);
String firstName = separedLine[0];
String lastName = separedLine[1];
String gender = separedLine[2];
return person.withFirstName(firstName).withLastName(lastName).withGender(gender).create();
}
Now you can change the argument order oder add new fields to person without creating a function with 10 parameters. The parser interface is simpler now, too.

Answer 2

There is no way to do that what I wanted. However two other solutions is possible. Use a lambda instead of PersonFactory::create or create a new functional interface.
Here is the result :
New functional interface
#FunctionalInterface
public interface TriFunction<A, B, C, D> {
public D apply(A a, B b, C c);
}
Add a function parseLine with my new functional interface
public class CsvPersonParser {
// Currying style
public Person parseLine(String line, String separator, Function<String, Function<String, Function<String, Person>>> creator) {
String[] separedLine = line.split(separator);
String firstName = separedLine[0];
String lastName = separedLine[1];
String gender = separedLine[2];
return creator.apply(firstName).apply(lastName).apply(gender);
}
// New Functionnal interface style
public Person parseLine(String line, String separator, TriFunction<String, String, String, Person> creator) {
String[] separedLine = line.split(separator);
String firstName = separedLine[0];
String lastName = separedLine[1];
String gender = separedLine[2];
return creator.apply(firstName, lastName, gender);
}
}
My main class with solutions
public class App {
public static void main(String[] args) {
final String DATA_FILE_SEPARATOR = ",";
final String FAKE_CSV_LINE = "Jean,Dupont,M";
CsvPersonParser csvParser = new CsvPersonParser();
Person person;
// Use curryling style
person = csvParser.parseLine(FAKE_CSV_LINE, DATA_FILE_SEPARATOR, f -> l -> g -> PersonFactory.create(f, l, g));
System.out.println("Currying style : " + person.getFirstName() + " " + person.getLastName() + " " + person.getGender());
// Use new functionnal interface
person = csvParser.parseLine(FAKE_CSV_LINE, DATA_FILE_SEPARATOR, PersonFactory::create);
System.out.println("TriFunction style : " + person.getFirstName() + " " + person.getLastName() + " " + person.getGender());
// Use lambda style
person = csvParser.parseLine(FAKE_CSV_LINE, DATA_FILE_SEPARATOR, (a,b,c) -> PersonFactory.create(a, b, c));
System.out.println("Lambda style : " + person.getFirstName() + " " + person.getLastName() + " " + person.getGender());
}
}