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Extending Object-Oriented PHP

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Extending a Class

3:03 with Alena Holligan

To inherit ALL the abilities and attributes of another class, we use the keyword "extends ".

Key Concepts

  1. Use the Keyword extends
  2. You can only extend from one class at a time.
  3. A child class will "inherit" all the attributes and actions of a parent

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    Let's jump right into code and see what it takes to extend a class. 0:00
    The classes for this project are stored in a folder named classes. 0:04
    In that folder is a listing ListingBasic class. 0:08
    This is the class we're going to extend. 0:11
    So let's take a look at what the class includes. 0:13
    There are some private properties, a constructor that sets those properties, 0:18
    and the getters and setters for each of those properties. 0:23
    There's also a method named two array 0:25
    that turns the object properties into an associative array. 0:28
    Let's create our new class in the classes folder. 0:32
    We'll name it ListingPremium. 0:37
    To build a class, we use the keyword class, followed by the name of our class. 0:47
    To inherit the abilities and 0:53
    attributes of another class, we then use the keyword extends. 0:55
    Followed by the name of the class we wish to extend, ListingBasic. 1:01
    We'll add the curly braces but leave this new class empty. 1:07
    Before we do anything else let's try using this new child class. 1:12
    Open classes Collection.php. 1:17
    This is the main controller for our application. 1:20
    This class takes a connection to a database on construction. 1:23
    It also has a method for selecting listings from the database. 1:27
    This method calls the addListing method, that adds a listing and 1:32
    returns a listing object. 1:37
    For right now, all we're going to do is change the class used. 1:40
    From ListingBasic to ListingPremium. 1:44
    Before this will work I need to make this new class available to the application. 1:50
    Open inc, config, this file performs some of the basic tasks for our application. 1:54
    We start a session Include the classes, connect to the database, and finally, 2:03
    create a directory object by passing the connection to our collection class. 2:08
    Lets copy the listing basic include. 2:13
    And we'll change it to ListingPremium. 2:19
    Now lets preview this site in a browser. 2:25
    Even though we didn't add any code to our ListingPremium's class, 2:29
    the site still functions exactly the same. 2:34
    Let's go back to our ListingPremium class. 2:37
    As you can see, this is in fact empty. 2:43
    However, we use the extend keyword to extend from ListingBasic. 2:47
    ListingBasic is the parent class and ListingPremium is the child class 2:53
    that inherits all the abilities and attributes of the parent. 2:58

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