Method reference in Java 8

Question

public class Car {

    private int maxSpeed;

    public Car(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public int getMaxSpeed() {
        return maxS         


        

Answer 1

Let's look at Function in detail:

Interface Function {

    default  Function   andThen(Function after){}

    R   apply(T t);

    default  Function   compose(Function before){}

    static  Function    identity();

}

note the R apply(T t); Applies this function to the given argument.

Function function = Void::?????;
Void voidInstance = null;
function.apply(voidInstance);

This doesn't make sense. You want to pass a Void so that the function of the Void is applied ?

A few illustrative examples of what compiles as a function

note that c->c.getMaxSpeed() and Car::getMaxSpeed are syntactically equivalent if the method is an instanceMethod. For non-static-methods the first argument is infered from the type who's method is used, and needs to be provided later (as the instance which the method will be executed on/applied on).

public class Car {

    private int maxSpeed;

    public Car(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public int getMaxSpeed() {
        return this.maxSpeed;
    }
    public Void setMaxSpeed() {
        this.maxSpeed = 12;
        return null;
    }
    public static int intStaticFunction(Void v) {
        return new Random().nextInt();
    }
    public static Void voidStaticFunction(Void v) {
        return null;
    }
    public static void main(String[] args) {
        final Car carX = new Car(155);
        final Car carY = new Car(140);

        final List cars = new ArrayList<>();
        cars.add(carX);
        cars.add(carY);

        cars.sort(Comparator.comparing(Car::getMaxSpeed));
        final Function function1 = c->c.getMaxSpeed();
        final Function function2 = Car::getMaxSpeed;
        final Function function3 = Car::setMaxSpeed;
        final Function function4 = n->n;
        final Function function5 = n->5;
        final Function function6 = Car::intStaticFunction;
        final Function function7 = Car::voidStaticFunction;
        final Function function8 = function1::apply;
        final Function function9 = function2::apply;
        System.out.println(function1.apply(carX));
        System.out.println(function2.apply(carX));
        System.out.println(function8.apply(carX));
        System.out.println(function9.apply(carX));
        System.out.println(function3.apply(carX));
        System.out.println(function1.apply(carX));
        System.out.println(function2.apply(carX));
        System.out.println(function8.apply(carX));
        System.out.println(function9.apply(carX));
        System.out.println();
        System.out.println(function4.apply(null));
        System.out.println(function5.apply(null));
        System.out.println(function6.apply(null));
        System.out.println(function7.apply(null));
    }
}