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What is a class?

From: Object-Oriented Programming with PHP

Video: What is a class?

While primitives have fixed data structures, objects in comparison can seem loose, in that they can have any number of properties. To give structure to an object, I can use a class. A class is a blueprint that defines the structure of an object. Objects are created in the exact same way using these class blueprints. This way, I know that when a class is used as a blueprint for an object, the structure of each object won't be different. Each class modularizes program functionality by separating features with as little overlap as possible.

What is a class?

While primitives have fixed data structures, objects in comparison can seem loose, in that they can have any number of properties. To give structure to an object, I can use a class. A class is a blueprint that defines the structure of an object. Objects are created in the exact same way using these class blueprints. This way, I know that when a class is used as a blueprint for an object, the structure of each object won't be different. Each class modularizes program functionality by separating features with as little overlap as possible.

Classes have attributes, which are the data structure for properties. There is a tiny technical difference between attributes and properties, but it's so minor that even the official PHP documentation uses the terms kind of interchangeably, and prefers properties. So, we'll also use properties. Classes also define behaviors, which are implemented as methods. A method is a subroutine that works on an object. I like to think of methods like a function that's contained within a class. Objects are instances of a class, meaning each occurrence of an object of a particular class has all the properties and behaviors of that class.

The individual properties will be the same, but the value stored in the properties may differ. As an example, I'm going to define a class for an address. The class address has several properties like the city, and subdivision, and has the behavior of being able to look up a postal code given the values of those properties. Therefore, every instance of class address will have those properties and behavior. I'm going to apply this address class to the real world using two instances. The first instance can represent Phoenix, Arizona, and the second instance can represent Columbus, Ohio.

As each object is an instance of class address, I know that they should have at least a city and subdivision. And, I know that it has the behavior of postal code lookup. I can't anticipate the contents of the object properties, but I can anticipate their format, and how to access them. This seems like a lot of work. I know that I can write code that works perfectly fine without defining classes with properties and behaviors. So, why bother using object-oriented programming?

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Object-Oriented Programming with PHP

37 video lessons · 17429 viewers

Jon Peck
Author

 
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  1. 4m 10s
    1. Welcome
      39s
    2. Exercise files
      2m 16s
    3. What you should know
      1m 15s
  2. 7m 47s
    1. What is an object?
      2m 6s
    2. What is a class?
      2m 7s
    3. Why should you use object-oriented programming?
      2m 14s
    4. The history of object-oriented PHP
      1m 20s
  3. 16m 40s
    1. Defining a class
      2m 58s
    2. Defining class properties
      3m 26s
    3. Creating a method and exploring object context with $this
      2m 50s
    4. Instantiating an object and accessing its contents
      3m 19s
    5. Specifying the visibility scope
      4m 7s
  4. 15m 51s
    1. What is a magic method, and do I need one?
      2m 23s
    2. Overloading property access
      6m 37s
    3. Customizing object construction
      4m 34s
    4. Standardizing object rendering as a string
      2m 17s
  5. 20m 54s
    1. Using the static keyword
      3m 36s
    2. Leveraging scope resolution operators
      1m 10s
    3. Setting constant values
      2m 47s
    4. Implementing static methods
      5m 43s
    5. Creating a database class
      7m 38s
  6. 26m 19s
    1. Extending your class
      6m 8s
    2. Abstracting classes
      5m 57s
    3. Sharing interfaces using polymorphism
      4m 39s
    4. Overriding methods, properties, and constants
      3m 25s
    5. Cloning and comparing objects
      2m 51s
    6. Referencing objects
      3m 19s
  7. 14m 52s
    1. Leveraging standard class objects
      2m 42s
    2. Retrieving objects from the database
      5m 41s
    3. Error handling with exceptions
      2m 6s
    4. Customizing PHP exceptions
      4m 23s
  8. 8m 2s
    1. Identifying the singleton pattern
      1m 42s
    2. Using the factory method pattern
      1m 51s
    3. Implementing a strategy pattern
      4m 29s
  9. 2m 57s
    1. Looking forward to namespaces
      47s
    2. Next steps
      1m 6s
    3. Goodbye
      1m 4s

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