WEBVTT

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Hello again! In this video, we are going to look at classes and inheritance. When we are working with classes

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in programs, we often find there are some classes which are related, or represent similar concepts.

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For example, with graphical shapes, they will all have some position on the screen.

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We can draw them, we can fill them in with different colours.

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We can rotate them, and so on. With document elements, such as text, tables and diagrams,

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we can format these.

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We can move them around, we can zoom in.

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With input streams in the C++ library, we can process input from different sources and convert it to data.

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And we can use a class hierarchy to express these relationships between different classes, and make

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it easier to reuse code between them.

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So, for example, with our shapes, we could have a basic shape, and then some more specialized shapes

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like circles, square and triangle.

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So this is a hierarchy of shape classes.

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For input

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streams, we can have istream as the basic input stream, and then ifstream is specialized for working with

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files, and istringstream is specialized for working with strings.

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In computer science, trees have their roots at the top and class hierarchies have their base at the

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top.

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So the class at the top of the hierarchy - the shape or the istream - is called the base class.

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So the base class is the most generic or basic version. The classes which come below this are known as derived

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classes, or subclasses of the base class.

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We say that they "inherit from" the base class or are "derived" from it.

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And these are more specialized versions of the base class, or classes which have more features. Enhanced

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versions.

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With shape, we have circle, triangle, square, which are derived classes from shape.

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So these are all specific kinds of shape.

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For istream, we have ifstream and istringstream, and these are more specialized input streams.

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The relationship between the classes at the different levels in the hierarchy is called inheritance

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in terms of object modelling, this represents an "is-a" or "is-kind-of" relationship between the classes.

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So an istringstream is a kind of istream, and a circle is a shape.

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Okay, so that is it for this video.

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I will see you next time, but until then, keep coding!