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[MUSIC]

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Welcome, I'm Alena.

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In this course we'll be extending from
the knowledge learned in a previous course

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to look at additional relationships
in the structure on our code.

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Laziness is one of the great
virtues of a programmer,

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we don't want to write the same
code over and over again.

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This is why one of the core concepts
of object oriented programming

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is aimed directly at reducing the amount
of repetition that you have to do.

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It's called inheritance.

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At its simplest,
it means we can give a child or

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a subclass all the abilities and
attributes of a parent or superclass.

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This helps us to greatly reduce
the amount of code we need to write.

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Let's take these elephants for example.

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Each of these elephants could be
an instance of an elephant class.

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Each object would simply set specific
properties such as color and logo.

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Both are created using the same pattern or
class.

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But what happens when we
want to build a mammoth?

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Not only have we changed the type
of material that's used, but

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we've also added tusks.

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Continuing to modify the original pattern
to add more features, can get complicated,

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and make it more difficult to
create our simple base elephant.

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Then what happens when we want
to add additional designs?

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Such as an Elvis elephant.

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Instead, we can keep our original
pattern in our class, and

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then extend that class by creating
a child, or sub-class, which

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includes all the attributes of the parent,
while additionally adding features.

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As another example let's take a bike.

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We have properties such as frame color,
number of gears, and current speed.

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We also have methods that control
things such as brake, change speed, and

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change gears.

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Now let's say we want to
build an electric bike.

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An electric bike is a regular bike with
the addition of an electric drive system.

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We would need additional properties for
battery and

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motor and a method to control
the power such as change_power.

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Instead of adding these properties and
methods to the bike class we could create

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a child class named electric bike,
that extends the original bike class

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by giving the child access to
all the original properties and

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methods while allowing the child
to add these additional features.

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In this course, we'll write code to
extend a simple directory project.

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If you would like to practice
building the original directory, or

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would like a refresher of things
that are not covered in this course,

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please check the notes
associated with this video.

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Let's take a look at the project.

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The simple directory we'll be starting
with has a list of PHP Conferences

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with links to their website,
email, and twitter.

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We have the ability to edit and
deactivate a listing.

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We also have the ability
to add a new listing.

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ll We'be adding premium listings
which include a description and

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featured listings which also
include a code of conduct.

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These new listing types will be used on
the listing page, and also for the forms.

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Along with these features, we'll also
add additional styling and navigation.