public static void main(String[] args) {
    File[] files = new File("C:").listFiles(File::isHidden); // OK
    test(MyCass::mymethod); // Cannot make a static reference to the non-static method
}

static interface FunctionalInterface{
    boolean function(String file);
}

class MyCass{
    boolean mymethod(String input){
        return true;
    }
}

// HELPER
public static void test(FunctionalInterface functionalInterface){}

listFiles(File::isHidden)

listFiles(f -> f.isHidden())

MyCass myCass = new MyCass(); // the instance
test(myCass::mymethod); // pass a non-static method reference

test(new MyCass()::mymethod);

class MyCass{
   static boolean mymethod(String input){
       return true;
   }
}

new FunctionalInterface{
  boolean function(String file){
    return MyClass.mymethod(file);
  }
}

new FunctionalInterface{
  boolean function(String file){
    return _missing_object_.mymethod(); # mymethod is not static
  }
}

test(MyCass::mymethod); // Cannot make a static reference to the non-static method

test(v -> MyCass.mymethod(v)); // static access

class MyCass {
  static boolean mymethod(String input) {
    return true;
  }
}

public static void main(String[] args) {
  MyCass myCass = new MyCass();
  test(myCass::mymethod);
}