CodeGym/Java Forum/Upcasting and downcasting. Basia and Diego describe it in...

Level 17

17.05.2021
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Upcasting and downcasting. Basia and Diego describe it in a contradictory way.

So, I've read three lessons about it and I am very confused. Why? Because it seems that in 1 lesson with Diego topic is described contradictory to 2 lessons with Basia. Which way is good? Lessons with Basia describes it in one way: https://codegym.cc/quests/lectures/pl.questcore.level04.lecture03 https://codegym.cc/quests/lectures/pl.questsyntax.level10.lecture03

Object object = new Tiger();

- upcasting example

byte a = 115;
int b = a;

- upcasting example as well And then Diego describes it in contradictory way: https://codegym.cc/quests/lectures/pl.questsyntax.level10.lecture06

Integer i = 123;
Object o = i;

- and this is how ~~upcasting~~ downcasting in Diego's version looks like. It seems to be what Basia would describe as upcasting.

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Guadalupe Gagnon

Level 37 , Tampa, United States

19 May 2021, 16:44

This isn't the full code. The narrowing conversions are described as such:

public static void main(String[] args)
{
     // !! this line is a widening conversion but it is NOT the demonstration !!
    Object obj = new Tiger();

    // these are the lines being demonstrated for narrowing
    Animal animal = (Animal) obj; // this line narrows obj to Animal
    Cat cat = (Cat) obj; // this line narrows obj to Cat
    Tiger tiger = (Tiger) animal; // this line narrows animal to Tiger
    Tiger tiger2 = (Tiger) cat; // this line narrows cat to Tiger
}

hidden #10719670

Level 17

19 May 2021, 17:14

Basia lessons are correct. The problem is with lesson with Diego where he describes everything opposite of what should be, narrowing as widening and vice versa (at least version in polish). Link to the lesson: https://codegym.cc/quests/lectures/pl.questsyntax.level10.lecture06

Guadalupe Gagnon

Level 37 , Tampa, United States

19 May 2021, 17:22

I can't read Polish, so that may be the case with the Polish version, but here is those same examples in English. These are all correct:

hidden #10719670

Level 17

19 May 2021, 17:24

Then translation is wrong. In your example everything is correct. In my it is opposite of what should be.

Guadalupe Gagnon

Level 37 , Tampa, United States

19 May 2021, 17:33

I'm sure they will fix it in a future update. There were some bugs in the tasks and incorrect descriptions in some of the lesson in the English version when I started this course (in 2018) that have all been corrected. They may see this thread, though it probably wouldn't hurt to message the admins in the case that they are unaware of the mistake.

hidden #10719670

Level 17

19 May 2021, 17:36

Hopefully. After few days of digging into it I understand it now. But if they'll correct it, at least somone in the future will benefit from this.

Guadalupe Gagnon

Level 37 , Tampa, United States

19 May 2021, 17:53

Feel free to message me if you have any Java questions. I talk with quite a few people on this site. I can recommend some good resources (check my post for some good videos(in English though): forum post) I usually am on most days, but will answer as soon as I return if I am not.

hidden #10719670

Level 17

19 May 2021, 17:57

Thanks!

John Squirrels Website Admin at CodeGym

20 May 2021, 06:47

We'll correct it soon. Poprawimy ten błąd wkrótce.

Artem Divertitto Senior Android Developer at United Tech

18 May 2021, 07:03

Integer i = 123;
Object o = i;

It's the same that

Tiger tiger = new Tiger();
Object object = tiger;

hidden #10719670

Level 17

18 May 2021, 10:35

My mistake. Diego describes it as downcasting not as upcasting. I corrected it in post above. So it's the opposite of what Basia said.

Jurij Thmsn

Level 29 , Flensburg, Germany

18 May 2021, 06:36

Like a lot of other people who commented on this problem, I was very confused by the contradicting way this topic was described in the course, as well. I recommend to re-learn this topic with other sources, otherwise you'll just be confused. e.g.: https://www.codejava.net/java-core/the-java-language/what-is-upcasting-and-downcasting-in-java

hidden #10719670

Level 17

18 May 2021, 10:42

It seems to me that Diego writes exactly opposite of what should be. Do you think, if I just exchange upcasting and downcasting in that article, everything will be correct?

Jurij Thmsn

Level 29 , Flensburg, Germany

18 May 2021, 12:43

Maybe, but I'd rather rely on other sources. Just exchanging the terms in the article might result in some other errors.