package functional;

@FunctionalInterface
interface Functional {
 String goodbye(String arg);
}


interface FunctionalNoAnn {
 String goodbye(String arg);
}

/*
@FunctionalInterface
interface NotFunctional {
 String goodbye(String arg);
 String hello(String arg);
}
Produces error message:
NotFunctional is not a functional interface
multiple non-overriding abstract methods
found in interface NotFunctional
*/


/**
 * @Author ZhangGJ
 * @Date 2020年05月08日 17:32
 */
public class FunctionalAnnotation {
 public String goodbye(String arg) {
 return "Goodbye, " + arg;
 }

 public static void main(String[] args) {
 FunctionalAnnotation fa = new FunctionalAnnotation();
 Functional f = fa::goodbye;
 FunctionalNoAnn fna = fa::goodbye;
 // Functional fac = fa; // Incompatible
 Functional fl = a -> "Goodbye, " + a;
 FunctionalNoAnn fnal = a -> "Goodbye, " + a;
 }
}