Htykuut

I have no idea why it's not working.

Error message in eclipse:
The method test(Fruit, capture#1-of ? extends Fruit) in the type BiPredicate is not applicable for the arguments (Fruit, Mango)

import java.util.function.BiPredicate;



public class PredTest {



    public static void main(String args) {



        class Fruit {

            public String name;

            public String color;

            Fruit(String name) {this.name = name; }

        };



        class Apple extends Fruit {

            Apple() {super("Apple");}

        };

        class Mango extends Fruit {

            Mango() {super("Mango");}

        };



        BiPredicate<Fruit, ? extends Fruit> tester = (f, nf) -> {

            System.out.println(nf.name);

            return true;

        };

        Fruit f = new Fruit("Not named");

        Apple a = new Apple();

        Mango m = new Mango();



// ########### I see error in the below line

        System.out.println(tester.test(f, m));



    }



}

Suppose you changed your lambda expression to:

    BiPredicate<Fruit, ? extends Fruit> tester = (Fruit f, Apple nf) -> {

        System.out.println(nf.name);

        return true;

    };

Would you still expect the compiler to allow passing a Mango to this BiPredicate?

Based on the compile time type - BiPredicate<Fruit, ? extends Fruit> - of tester, the compiler doesn't know if Mango is allowed, so it doesn't allow it.

Changing your BiPredicate to:

BiPredicate<Fruit, ? super Fruit> tester = (f, nf) -> {

    System.out.println(nf.name);

    return true;

};

will eliminate the compilation error.