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So let's start by seeing how patterns are defined. So

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what is the format of the pattern definitions. If we look

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at the Gang of Four's book we can see that these

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definitions contain a lot of information. In fact, what I'm listing

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here is just a subset of this information. In this lesson,

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what I want to do is to focus on four essential

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elements of a design pattern. It's name, the intent which is

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the goal of the pattern. The pattern's applicability which is the

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list of situations or context in which the

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pattern is applicable. I also want to cover the structure

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and participants. Which is the static model that describes

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the elements, so normally the classes or the object

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involved in the pattern. In addition to that

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the structure also describes

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the relationships, responsibilities and collaborations

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among these classes or objects. Finally what I want

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to cover is sample code. So examples that illustrate

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the use of patterns.