Functional Interface

FI.java

@FunctionalInterface
public interface FunctionalI {
   void abstractMethod();

   default String defaultMethod() {
       return "defaultMethod";
   }

   static String staticMethod() {
       return "staticMethod";
   }

   boolean equals(Object obj);
}

class Main {
   public static void main(String[] args) {
       FunctionalI a = () -> System.out.println("test");
       a.abstractMethod();
       System.out.println(a.defaultMethod());
       System.out.println(FunctionalI.staticMethod());
   }
}