What are Classes, Objects, and Constructors?

Key Takeaways

Are you confused by the terminology of object-oriented programming such as constructor, class, new keyword, instantiation, and so on? Well, in today's video, I'm going to be going over all of the basics of object-oriented programming so you no longer get confused by these words. Let's get started now. Easily the most confusing part about object-oriented programming is the differences between a class and an object. And simply put, a class is going to be a blueprint. Essentially, it defines all of the methods, it defines all of the different properties that our objects can have, but it doesn't actually give it any data or information. It's just a blueprint, a holder for what our object is going to look like. And an object on the other hand is an instantiated version of a class. Essentially, it's a specific version of a class that has all of the extra information filled in such as the different values for the properties and what all the methods are going to return. So, this is very similar to how a house and a blueprint work. A blueprint is going to be the same as a class. The blueprint defines what we want our house to look like. In general, it's going to be where the walls go, where the different rooms are, but the blueprint doesn't tell us what color the house is going to be or what furniture is going to be in that house. The actual object itself, or the house in this instance, is going to tell us what the color is and what the different furniture is going to be inside of it, but not the blueprint, which in our case is the class. And then, moving on from there, we have the new keyword. The new keyword is how we actually take a class and turn it into an object. And to do that, we use the constructor inside of the class. To make all of these different points concrete, let's look at an example in actual code using JavaScript. To illustrate this, we just have a blank JavaScript file, which we are going to first create a class in, which is going to be our blueprint. So, we're going to create a class. We're going to call it house because this class is going to be used to create house objects. And inside of here, what we need is a constructor. So, we can just type the keyword constructor, and the constructor is going to take all the parameters we want to put into our house when we create a new instance or a new object of that house. So, for example, we want to know the color of our house because every house we create is going to have a different color. And then inside of here, we can just set that color. So, we can say this.color is equal to color. And this is just going to save our color onto our house object itself that we're creating. Now, all we can do is come down here. We can create a variable. We're just going to call it house object because this is going to be the actual instantiated object of our house. We just want to set that equal to new house. And the reason we use this new keyword is because by putting the new keyword before the name of the class, which in our case house, it's going to call the constructor with everything we pass into the brackets here, these curly or these parentheses here. So, if we pass in a color, for example, red, now this is going to pass this red variable in here for color, and it's going to set it on our house. So, this is going to create us a new version of this house class, which is going to be an object, and it's going to save it in this house object variable. And for example, if we wanted to have a function on our house that got us all the furniture in our house, we could just say get furniture. And we could just say it takes nothing. And in here, it's just going to return us our furniture, which in our case is just a single sofa. And this function is going to be shared between all the different instances or all the different objects of our house class. So, let's create another house object here. We'll call it house object two. And we're going to make this one blue. And now what we want to do is we actually want to log out some information about our houses. So, we can come down here, and we can just console.log our first house object. And we just want to get the color of it. And we're also going to call that function, which is get furniture, and see what this is returning. We're going to do the exact same thing but for our second house down here. So, we're going to say house object two and two. Save that. And now let's actually see what that returns. If we see over here, we have red being returned as the color of our first house, and sofa being returned for our furniture. And you can see our blue house has blue being returned as the color. And again, sofa is being returned for the furniture because this function is on the definition of the class, which means it's shared between all the different objects, house object one and house object two. But, this color is being variable. It got passed into the constructor. So, this is being changed based on what we passed in here for our new house. In our case, the first one is red and the second one is blue. If you want to see more videos of me simplifying programming terminology, let me know down in the comments and I can turn this into a full series. Also, let me know what other terms you want me to cover in the future. Thank you very much for watching this video and have a good day.