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Jian Chen
4,938 PointsWhat is so special about an instance variable?
So people make an instance variable like this, Class variable = new class. But what is the difference from just declaring it as, Class variable = somevalue ? Don't they both have the same method and states because they both belong to the same class?
2 Answers
Steve Hunter
57,712 PointsHi Jian,
The convention doesn't work quite as you think in that example.
An instance of a class requires building, otherwise knows as constructing. Take the Story class in this video as an example.
You can create the variable, like you say, Story myStory; does that. But this doesn't fill the instance with anything. I guess it just reserves a Story sized chunk of memory, but leaves it blank.
You then assign the contents of a Story instance by calling the class constructor. This creates an actual instance, depending on the constructor you have created and any parameters it takes. So, new Story() creates a real instance of a Story but that has no name, or anywhere to live in memory. Hence, you assign it to the chunk of memory named myStory by completing the instantiation and assignment such as:
Story myStory = new Story();
I hope that makes sense. It probably isn't wholly technically correct but it's my best shot!
Shout if you need anything more.
Cheers,
Steve.
Steve Hunter
57,712 PointsI think the built-in class types like String do the heavy lifting behind the scenes. The code is there, we just don't see it.
I've never tried doing that, either - might be an interesting experiment!
Steve.
Steve Hunter
57,712 PointsTried it, and you get a warning about not needing to use the constructor.
Jian Chen
4,938 PointsThank you, Steve. I understand it now.
Jian Chen
4,938 PointsJian Chen
4,938 PointsThank you Steve, I really appreciate your help and you did clarify to me what "new" does. Do you know why we don't create an instance for the String class, as we usually just write ' String variable = "someChar"; ' and not as ' String variable = new String then ' variable = "someChar" '?'