Class Inheritance

Quick reference

• 00:04 I want to finish talking about classes with something called class inheritance.
• 00:08 Now, we could talk about classes for hours and hours and hours.
• 00:11 I just wanted to sort of give you a very quick introduction to classes,
• 00:15 explain some key concepts, and then we'll move on.
• 00:17 So class inheritance is basically, you can actually inherit something from one class
• 00:22 into another class, so that's what we're going to look at in this video.
• 00:26 So we have our Square class, we've got our attr_assessor, got our initialize,
• 00:31 our area.
• 00:31 So let's go ahead real quick and just create another class, and
• 00:35 let's call it paint.
• 00:39 All right, and I'm not going to do all the initialize, and all the stuff.
• 00:42 Let's just create a quick method called color, and
• 00:47 let's give it an instance variable of color, and set it = blue.
• 00:52 So just a very, very simple class, like I said, just for
• 00:57 purposes of showing this stuff.
• 01:00 So let's initialize our class.
• 01:03 Let's go my_paint = Paint.new and there's no
• 01:08 parameters that we need to pass in, so we're good to go.
• 01:13 So now, we can call a puts my_paint.color.
• 01:20 And if it works correctly, it should just print out blue.
• 01:23 Let's save this and hit Reload.
• 01:25 And sure enough, we see blue, and we're still getting code from our last couple of
• 01:29 videos, but this is what we've got blue.
• 01:31 So all we have in this class, just very, very simple, and
• 01:34 all it does is print out blue.
• 01:36 Well, that's not that useful, but we can actually pull
• 01:39 in all the stuff from this class into this class, and then use it if we want.
• 01:43 And to do that, it's really simple.
• 01:45 All we do is this less than sign, and then you just type in the name of your other class.
• 01:51 In our case, I type S, it already knows that we want square.
• 01:54 So now we can come down here, and let's just inspect this,
• 01:57 we're probably going to get an error here, I'll show you why.
• 02:01 So yeah, we get an error, and
• 02:03 that's because this class requires parameters to be passed in.
• 02:07 And when we initialized our new paint class, we didn't pass any parameters.
• 02:12 So let's pass in the parameter of 30, so that's going to be our side length, right?
• 02:16 Now if we save this and run it again, we get just this @side_length=30.
• 02:22 And you can see our Paint class now has side_length of 30 as a part of it,
• 02:27 even though that's in the Square class, not the Paint class.
• 02:32 So just by doing this, boom, we've sucked in all the stuff from the Square class
• 02:36 into our Paint class, and we can do stuff.
• 02:39 So we can go paint.color, like we did earlier, and we get blue.
• 02:44 We can also go paint.area, because that's a method inside the Square class, right?
• 02:50 So if we save this, boom 900, because area is 30 times 30, or 900.
• 02:57 What else do we have here?
• 02:58 Area initialize, we've got our getters and our setters.
• 03:01 We can use our getters and our setters now with our paint instance,
• 03:05 this instance of this Paint class that we have, this my_paint.
• 03:08 So that's just a very, very quick primer on class inheritance.
• 03:12 The main concept is you just add it right here, and
• 03:15 we'll use this a lot in Ruby on Rails.
• 03:17 This is obviously not a Rails course, but when you see Ruby on Rails, they do a lot
• 03:21 of class inheritance with all their stuff, and you'll see that a lot there.
• 03:25 You'll use it for other things as well.
• 03:26 But anyway, that's class inheritance, that's classes.
• 03:30 I know that was sort of a whirlwind last few videos worth of stuff, and
• 03:33 you might want to go back and watch all these class videos.
• 03:35 Again, it's only until you start using these, and
• 03:37 then things start clicking into place, and it makes sense.
• 03:40 It's just one of those things, classes take a while for people to sort of wrap
• 03:43 their brains around, so don't feel bad if you're kind of struggling to get it.
• 03:46 In the next video, we're going to look at files, and opening a file.

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