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In this video, we'll learn
some of the terminology and

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notation used with inheritance.

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The terminology we use is
pretty straightforward, but it's

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important that it's clear since
you'll be using it throughout

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your career as a c++ developer.

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First, let's review inheritance.

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As we've already seen, inheritance
is the process of creating new

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classes from existing classes.

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It's a mechanism that allows
us to reuse existing code.

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When we use inheritance to
create a new class, there may

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be several classes involved.

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In this course, we'll mainly talk
about single inheritance that

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is when we create a new class
based on another single class.

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Multiple inheritance is when
we create a new class from

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two or more other classes.

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The classes that are involved in
the inheritance relationship also

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have terms associated with them.

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The base class is the class
being extended or inherited from.

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This class is also referred to as
the parent class or super class

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in the inheritance relationship.

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The derived class is the class that's
being created from the base class.

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This class will inherit the attributes
and operations from the base class.

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And this class is also referred to
as the child class or the subclass.

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You can see in the diagram, the
commonly used notation used to

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express this inheritance relationship.

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We draw a solid line between the
base class and the derived class

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with a closed unfilled arrowhead or
triangle pointing to the base class.

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This is a uml class diagram and
can also show much more information

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about the classes we're modeling.

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A very important concept to
understand is that of an is a

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relationship with object-oriented
programming and inheritance.

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When we use classic or public
inheritance, our derived

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classes are generally subtypes
of their base classes.

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This implies an is a relationship.

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So a circle is a shape, a
savings account is an account.

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This very simple concept will provide
us with a great deal of power.

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We'll learn how to leverage this
is a relationship in the next

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section of the course when we
learn about polymorphic functions.

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Generalization is about combining
similar classes into a single,

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more general class based on
the class's common attributes.

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The more general class is obviously
more abstract and can therefore

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potentially be reused more easily.

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Specialization is the
opposite of generalization.

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This is about creating new
classes from existing classes.

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And these new classes generally
add attributes and operations

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to the already inherited ones.

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As programmers and designers, we use
both generalization and specialization

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to create inheritance hierarchies.

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Inheritance hierarchies is how we
organize our inheritance relationships

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so that we can more effectively
organize and reuse our code.

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Let's see a simple example.

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In this example, we have classes
a b c d, and e and we have public

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inheritance that is is a relationship
between derived and based classes.

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You can see that class a is not
being derived from any other class.

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This class is often referred to as
the root class in the hierarchy.

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B is derived from a, c is also
derived from a, d is derived

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from c and e is derived from d.

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You can see the class
hierarchy in the diagram.

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Notice that the higher up
we go in the hierarchy, the

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more general our classes are.

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And the lower we go in our hierarchy,
the more specialized they are.

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Also notice the is a relationships.

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In this example, b is an a.

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C is also an a since they're both
derived from the class a, and e is a

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d because e is derived from class d.

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Now notice that e is also a c
since inheritance is transitive.

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In fact, in this
example, e is also an a.

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However, class b is not a c.

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There is no inheritance relationship
directly between b and c.

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Let's look at a more concrete example.

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In this example, we have
a root class person that's

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the most general or abstract
class in this class hierarchy.

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We can see that student
is derived from person.

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So a student is a person and
inherits the attributes and operations

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of the person class.

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We also see that employee is a
person, and faculty staff

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and administrators are derived from
employee, so they are employees.

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In fact, they're also persons.

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But notice that a student is not an
employee in this class hierarchy.

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Also notice that the is a
relationships are not bi-directional.

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For example, a person is not
necessarily an employee because

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they could be a student.

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You can see how useful a class
diagram can be since it provides a

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high level structural overview of
the classes and the relationships.

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In the next video, we'll look at
another way of reusing classes

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in c++ called composition and see
how it differs from inheritance.