Object-oriented programming has become the most widely used approach to software development. Learn about the core concepts of object-oriented programming and how they are implemented using objects, classes and methods in this video lesson.
What Is an Object in Programming?
Object-oriented programming, or OOP, is an approach to problem solving where all computations are carried out using objects. An object is a component of a program that knows how to perform certain actions and how to interact with other elements of the program. Objects are the basic units of object-oriented programming. A simple example of an object would be a person. Logically, you would expect a person to have a name. This would be considered a property of the person. You could also expect a person to be able to do something, such as walking or driving. This would be considered a method of the person.
Code in object-oriented programming is organized around objects. Once you have your objects, they can interact with each other to make something happen. Let's say you want to have a program where a person gets into a car and drives it from A to B. You would start by describing the objects, such as a person and car. That includes methods: a person knows how to drive a car, and a car knows what it is like to be driven. Once you have your objects, you bring them together so the person can get into the car and drive.
Classes and Objects
A class is a blueprint of an object. You can think of a class as a concept, and the object is the embodiment of that concept. You need to have a class before you can create an object. So, let's say you want to use a person in your program. You want to be able to describe the person and have the person do something. A class called 'person' would provide a blueprint for what a person looks like and what a person can do. To actually use a person in your program, you need to create an object. You use the person class to create an object of the type 'person.' Now you can describe this person and have it do something.
Classes are very useful in programming. Consider the example of where you don't want to use just one person but 100 people. Rather than describing each one in detail from scratch, you can use the same person class to create 100 objects of the type 'person.' You still have to give each one a name and other properties, but the basic structure of what a person looks like is the same.
Methods and Functions
Once you have created objects, you want them to be able to do something. This is where methods come in. A method in object-oriented programming is a procedure associated with a class. A method defines the behavior of the objects that are created from the class. Another way to say this is that a method is an action that an object is able to perform. The association between method and class is called binding. Consider the example of an object of the type 'person,' created using the person class. Methods associated with this class could consist of things like walking and driving. Methods are sometimes confused with functions, but they are distinct.
A function is a combination of instructions that are combined to achieve some result. A function typically requires some input (called arguments) and returns some results. For example, consider the example of driving a car. To determine the mileage, you need to perform a calculation using the distance driven and the amount of fuel used. You could write a function to do this calculation. The arguments going into the function would be distance and fuel consumption, and the result would be mileage. Anytime you want to determine the mileage, you simply call the function to perform the calculation.
How does this differ from a method? A function is independent and not associated with a class. You can use this function anywhere in your code, and you don't need to have an object to use it.
Now, what if you were to associate the function with an object of the type 'car?' For example, you want to be able display the mileage of the car on the dashboard. In this case, the mileage calculation has become a method because it is a procedure associated with the car's class. Every time you create a new object of the type 'car' using the car class, this method will be part of the object. The action the car is now able to perform is to calculate mileage. It is the same calculation as performed by the stand-alone function but is now bound to the car.
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