Which objects are allowed in a method

Question

I have a general question. Let's say I have the following structure:

interface IFirst{}
class A implements IFirst{}
class B extends A{}

And furthermore the following class:

class TestClass{
    public dummy(IFirst data){}
 }

Which kind of Objects does the dummy-Method accept then?

it accepts instances of all classes which implement the `IFirst` interface (including `A` and `B` and other implementations if they exist), and it also accepts `null`. — Alex Shesterov, May 21 '17 at 17:36
by the way, the method signature syntax is not correct and it won't compile. — Alex Shesterov, May 21 '17 at 17:40

score 0 · Answer 1 · answered May 21 '17 at 17:36

Its simple, every Object that somehow implements the interface IFirst. In your example that is A and also B since B extends A which is an IFirst, so B is also an IFirst.

Here's another example, the following structure:

interface Animal
class Dog implements Animal
class Cat implements Animal
class Husky extends Dog
class SmallDog extends Dog
class Chihuahua extends SmallDog

Makes sense that everything is of type Animal here :)

Which objects are allowed in a method

1 Answers1