Question

How to call? How to do?

public class Test {
        public static void main(String[] args) {
            Test test = new Test();
            Animal a = new Animal("Animal");
            Dog d = new Dog(" BigDog ","yellow");
            Cat c = new Cat(" SmallCat ","black");
            test.f(a); test.f(d); test.f(c); //(1)
        }

        public void f(Animal a) {
            System.out.println("name :"+ a.name);

            if(a instanceof Dog) {
                Dog dog = (Dog)a;
                System.out.println("    "+ fursColor + "fur"); //!(2)!Error
            }
            else if(a instanceof Cat) {
                Cat cat = (Cat)a;
                System.out.println("  " + eyesColor + "eye"); //(3)!Error
            }
        }
    }

Ask Question:

(1) What’s the meaning of this?

(2) How to call “yellow”?

(3) How to call “black”?

Answer 1

(1) What’s the meaning of this?

The method f is using instanceof as it is not use polymorphic methods to select the right type.

Can you be more specific as to what you don’t understand.

(2) How to call “yellow”?

I assume you want is to retrieve the String in the field in dog with dog.fieldNameNotShownInYourExample as it did in a.name to get the name.

(3) How to call “balck “?

I assume it should be "black" but its the same as 2)