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Java Inheritance in Java Inheritance in Java Everything Inherits from Object

Phoenix S.
Phoenix S.
2,456 Points
Posted by Phoenix S.
Phoenix S.
2,456 Points

I think there's a bug in the first Inheritance quiz

When answering questions 4 of the first inheritance quiz my answers were marked correct in the editor and wrong upon submission. It's not really a huge deal but I want to know what's going on.

The blanks I filled in will be noted with **

Here's the code for Question 4: How would you fix this code?

public class Main {
    public static void main(String[] args) {
        Thing widget = new Widget();
        **((Widget)excuseId[1]) || ((Widget)excuseId[0]) || ((Widget)excuseId[]) || ((Widget)excuse)**.refuseToWork(); 
    }
}

class Widget extends Thing {
    String[] excuses = {"It's too heavy.", "I don't know how.", "You know I don't speak Spanish."};
    int excuseId = 1;

    void refuseToWork() {
        String excuse = excuses[++excuseId];
        System.out.println(excuse);
    }
}

class Thing {
    String purpose = "do stuff";

    void printPurpose() {
        System.out.println(purpose);
    }
}
Lauren Moineau
Lauren Moineau
9,483 Points

Hi Phoenix. Was your answer made up of all that is between ** or did you try 4 different times with each of the 4 (widget) excuseId[] you put there?

3 Answers

Lauren Moineau
Lauren Moineau
9,483 Points

Hi Phoenix. I think you got a green tick from the editor here because you cast the object, which was what was expected. However, I'm afraid your answer is indeed incorrect. When you write 

((Widget)excuseId[1].refuseToWork();

you are actually calling the refuseToWork() method on an excuse String, expecting an excuse String as an answer.

To know which object you should call a method on, just check where the method is implemented. Here, the refuseToWork() method is implemented in the Widget class. So we'll need to call that method on a Widget object.

In the main method, we do have an object called widget but it's actually a Thing. So we will need to cast it as a Widget in order for us to call the refuseToWork() method on it.

Now, you were absolutely correct in writing a double parenthesis to ensure we cast the object we call the method on and not the result of that method. So we should have:

((Widget)widget).refuseToWork();

I hope this helps :)

Phoenix S.
Phoenix S.
2,456 Points
Phoenix S.
Phoenix S.
2,456 Points

That does make sense! Thank you for explaining it to me! :)

Lauren Moineau
Lauren Moineau
9,483 Points

You're welcome :)

Phoenix S.
Phoenix S.
2,456 Points
Phoenix S.
Phoenix S.
2,456 Points

I tried 4 different times

Lauren Moineau
Lauren Moineau
9,483 Points

ok. Thanks

Laura Owens
Laura Owens
15,044 Points
Laura Owens
Laura Owens
15,044 Points

Thank you! I was struggling with that last night and re-watched the entire module but still didn't quite get it. Your answer is perfect :)

Lauren Moineau
Lauren Moineau
9,483 Points

You're welcome @Laura Owens :) I'm glad I could help.