Enthuware

Basically, when you do Supplier<MyProcessor> s = MyProcessor:new; you are telling the compiler to get you the constructor reference of the constructor that does not take any argument. This is because Supplier's functional method does not take any argument.

public void debug(){         System.out.println(name+":"+marks);     }
...
slist.stream().forEach(Student::debug);

admin wrote: ↑

Fri Sep 22, 2017 9:17 pm

forEach expects a Consumer<Student> i.e. an object of a class that implements Consumer with a method accept(Student s);

Now, Student::debug is a reference to an instance method of Student. When you pass this method reference to forEach, an inner class will automatically be created like this:

Code: Select all

class SomeClass implements Consumer{
    public void accept(Student s){
       s.debug();
    }
}

Notice that here, everything except the call to s.debug() is boilerplate (i.e. common to all). Since each iteration of forEach already has a reference to a Student object, the compiler can easily deduce that it needs to invoke the debug() method on that instance. For this reason, compiler is OK with a method reference Student::debug.

The key to understand here is that there are no objects at compile time. You are only giving a hint to the compiler about the object that will there at run time and based on this hint, the compiler automatically creates the anonymous class that invokes method on appropriate object.

interface FunctionalInterface2{

    int operation(int a, int b);
}

public class Calculator3 {

    int operate(int a, int b, FunctionalInterface2 functionalInterface2){
        return functionalInterface2.operation(a,b);
    }

    public static void main(String[] args) {
        Calculator3 calculator3 = new Calculator3();
        System.out.println(calculator3.operate(1,2,(a,b)->a+b));

        System.out.println(calculator3.operate(1, 4, new FunctionalInterface2() {
            @Override
            public int operation(int a, int b) {
                return a+b;
            }
        }));
    }
}