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Every class defines a new type. Objects are just instances of a type.
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We can't talk about objects
without talking about types.
0:00
You see every object is of a certain type.
0:02
Remember when we use strings,
ints, doubles before?
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They're called types because
they form the template for
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the values that are of that type.
0:12
In C sharp every value that a variable
can take on is an object, so
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we've already used a bunch of objects,
five, ten and
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23 are all objects of type int.
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3.14 10.5 100.2 are all
objects of type double.
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Hello Bob and We the People
are all objects of type string.
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These are all types that are built into
the C Sharp language and .net framework.
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We can create our own types though,
that's what classes are for.
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A class is the template for making
individual objects of a particular type.
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Each individual object that a class makes
is called an instance of that class.
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Remember we can use the words type and
class interchangeably.
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So we could also say that an object
is an instance of a type.
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You can think of classes
like a cookie cutter.
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And the cookies
are instances of that class.
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This cookie cutter makes
heart shaped cookies.
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So all the cookies that this cookie
cutter makes are of that type.
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Each of these cookies
is a distinct object,
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even though they're all
shaped like hearts.
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Also, just because we're
using the same cookie cutter,
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doesn't mean all of the cookies
have to look the same.
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We can make each heart shaped
cookie a little different.
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For example, we could add food
coloring to the dough, and
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have pink heart shaped cookies.
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The color is one of
the attributes of the cookie.
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Likewise, we can create
different objects from a class
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by changing the attributes of that class.
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Let's take a look at a graphical user
interface of a piece of software to get
1:53
an idea of how it's composed
of classes and objects.
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Take a look at the Chrome browser for
example.
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You're probably very familiar with
what a web browser looks like.
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But have you ever thought
about how it's put together?
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In the code for the Chrome browser
there's a class that models a tab.
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This tab that I'm pointing to right
here is just one instance of that class.
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I can make many tab instances.
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Each of these tabs is
a separate object and
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they're all created from the tab class.
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Each tab has a title attribute
that is different for each tab.
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They also have a behavior so
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that when they're clicked,
their content is shown in the Window.
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There's a menu class with that many
menu objects created from that class.
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There's a button class and many unique
objects created from the button class.
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I hope you're starting to get an idea of
what object-oriented programming is and
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how it's useful.
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In the next videos,we'll get to
see how this is all done in code.
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And hopefully things will
become even more clear.
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The concept of objects in code can be
a little difficult to understand at first.
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If after working through some code,
things still aren't making sense.
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I suggest watching this video again while
thinking about what we've done in code.
3:09
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