Simply Objects

What is Object oriented programming(OOP)?. As the name implies, its all about the Objects. But what does that really mean? Let’s look at some real-world examples to find out.Imagine an object that most people can relate to, a car.

How can we describe a car?

Well, it has certain attributes such as the color, make, model, year, mileage, and vin. Each of these attributes, make each car what it is.

In Object Oriented Programming, the features that describe an object, are called properties.

Behavior of an Object

The next question is, what are the actions a car can do, or can be done by the car?

Let’s take some of the obvious ones:

Car can carry passengers
Car can accelerate
Car can brake

In Object Oriented programming, these actions, are called methods. They allow the objects to do things, and, also provide a way to read/write the properties of the object.

For example - After you buy the car, you may decide you don’t like the color and want it repainted to white. In object oriented programming, we call these setter methods, which are just special methods for setting properties on an object. On the other hand let’s say we get stopped for a speeding ticket, and the officer wants to get the VIN number. You would read the VIN through a getter method.

Creating Cars/Objects

Now that we have properties, methods, and ways to read or set/change the properties through setter and getter methods, you may be wondering, how do we create the car/objects in the first place?

The obvious answer is, using a car factory or as referred to in object orientation, a constructor . A constructor is a special method which creates an object. After you’ve created an object, you have an instance of it. This process is called instantiation.

Example

Lets go back to the car example. We are at the factory, and we instantiate our car by using a constructor method to create it. This special method takes inputs for the model, color, and VIN number, and outputs a brand new car.

At this point , we’ll change terms, and instead of calling these objects, we’ll now call them classes. Example the Car Class

Classes are “blueprints” for creating a group of objects.
  – A car class to create car objects

The blueprint defines
  – The class’s properties as variables
  – The class’s behavior as methods

How can we create Trucks/ Buses ?

Now how do we create a Truck or a Bus. How can the above knowledge help us be more efficient at creating any type of Vehicle, not just a car. Using our previous example we can now have a class called vehicle, with all the properties and methods common to our three types of vehicles. This is called the parent class, and the three vehicles are it’s subclasses.

What’s important to note is that those common properties and methods only need to be defined in the parent class level. The children automatically have access to these, and so defining them there is not necessary. This concept is called inheritance.

Inheritance

In the subclasses, we only need to define the things that are unique to them. For example, for a truck the maximum amount of cargo is important, so this could be a property, and a bus may have a method to loadPassengers or unloadPassengers.

Also imagine that we started to produce other types of vehicles, the inheritance concept really makes things easier to add them, as we simply need to define the properties which are not already covered by the common vehicle class.

In OOP, you will sometimes have classes that are not intended to be used directly (such as our vehicle class in this example), but instead simply exist as a common parent. In these cases, it is meant for the subclasses to be used. In other cases, the parent and subclasses can be used. Or, subclassing can be a way for you to extend an existing class that you would like to add functionality to.

Summary

Will leave you with an expert from a 1994 Rolling Stone interview, where Steve Jobs explains exactly what object-oriented software is.

Interviewer: Would you explain, in simple terms, exactly what object-oriented software is?

Steve Jobs: Objects are like people. They’re living, breathing things that have knowledge inside them about how to do things and have memory inside them so they can remember things. And rather than interacting with them at a very low level, you interact with them at a very high level of abstraction, like we’re doing right here.

Here’s an example: If I’m your laundry object, you can give me your dirty clothes and send me a message that says, “Can you get my clothes laundered, please.” I happen to know where the best laundry place in San Francisco is. And I speak English, and I have dollars in my pockets. So I go out and hail a taxicab and tell the driver to take me to this place in San Francisco. I go get your clothes laundered, I jump back in the cab, I get back here. I give you your clean clothes and say, “Here are your clean clothes.”

You have no idea how I did that. You have no knowledge of the laundry place. Maybe you speak French, and you can’t even hail a taxi. You can’t pay for one, you don’t have dollars in your pocket. Yet, I knew how to do all of that. And you didn’t have to know any of it. All that complexity was hidden inside of me, and we were able to interact at a very high level of abstraction. That’s what objects are. They encapsulate complexity, and the interfaces to that complexity are high level.