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[MUSIC]

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It may surprise you to know that all types
in C# inherit from a common base class.

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That includes the classes
that we make ourselves.

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This common base class is system.object
and it has a lot to offer.

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In this part of the course,
we'll get to know this common class.

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System.Object offers
many excellent examples

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of how every class can take advantage
of polymorphism and overriding methods.

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To start,
let's take a look at the documentation for

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System.Object on
the Microsoft Developer Network.

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We can find this documentation
by searching for System.Object.

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Or you can click on the link
in the teacher's notes.

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Here it says that this is
the ultimate base class of

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all classes in the .NET Framework.

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It is the root of the type hierarchy.

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This is saying that all classes
inherit from System.object,

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even if we don't put :System.Object
in our class declaration.

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We can type it,

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but it isn't required because all
classes inherit from it anyway.

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System.Object provides
these eight methods.

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I'll briefly explain what
all these methods are and

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we'll go into depth on a few of them.

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First, we want to be familiar with
the symbols to the left of the names of

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the methods in the MSDN documentation.

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The pink cube which appears to be on
the move means that this is a method.

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The yellow S means that
the method is a static method,

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meaning it can't be called
on an instance of the class.

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Only the class itself.

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This little yellow key means
that the method is protected.

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So it can only be accessed from within the
class and classes that inherit from it.

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All of the non-static methods
except GetType are virtual methods.

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So they can be overridden in subclasses.

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Static methods cannot be
overridden in subclasses.

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GetType returns an object of type Type.

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This type with a capital T is a class that
contains information about an object type.

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Using GetType to get information
about an object type

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is commonly known as reflection.

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You may have heard that term before.

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Reflection is a topic for another course,
so I won't go into it here.

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Check the teacher's notes if
you'd like to learn more.

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Let's learn about these other methods.