Java8: About Functional Interface

Question

I would like to ask about the following piece of code related to Functional Interfaces. I am confused by:

Rideable rider = Car :: new

Is it creating a Rideable (interface) or Car (class) instance? If it is creating a Car object, the constructor new Car() (i.e. with no arguments) should be not existing, then how come this can be valid?

I Have been reading through this tutorial ,but still could not figure it out.

@FunctionalInterface 
interface Rideable {
  Car getCar (String name);
}

class Car {
  private String name;

  public Car (String name) {
    this.name = name;
  }
}

public class Test {
  public static void main(String[] args) {
    Rideable rider = Car :: new; 
    Car vehicle = rider.getCar("MyCar");
  }
}

Answer 1

Is it creating a Rideable (interface) or Car (class) instance?

It is creating an instance of (a class that implements) the Rideable interface.

The Rideable functional interface has a single method - getCar - that accepts a String argument and returns a Car instance.

The public Car (String name) constructor accepts a String argument and produces a Car instance.

Therefore the method reference Car::new (which in this case does not refer to a parameter-less constructor) can be used as implementation of the Rideable interface.

And if it helps to clarify the confusion, here's a lambda expression equivalent to the Car::new method reference:

Rideable rider = (String s) -> new Car(s);

or

Rideable rider = s -> new Car(s);