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3.26 DecoratedWordLibrary

Juppies 2 by Dr Heinz M. Kabutz

Our ShuffledWordLibrary and our ScrambledWordLibrary are quite similar. They both have a WordLibrary field called other, to which they delegate the method calls. Duplicate code is problematic, because if we make a mistake, this also gets duplicated. Instead of having to fix the code in a single place, we have to fix it everywhere.

We are going to create a DecoratedWordLibrary that looks similar to our ShuffledWordLibrary, but will be used as a common superclass for our ShuffledWordLibrary and ScrambledWordLibrary. What we are creating here is following a well-establish design pattern called the decorator pattern.

Our DecoratedWordLibrary has a field other that points to another WordLibrary, which is marked as final and is set in the constructor (auto generate this with ALT+Insert or right-click, Insert code). We then delete the three empty methods and delegate them to the other field, again with ALT+Insert or right click, Insert code.

Lastly, we mark our DelegatedWordLibrary as abstract, so that no one accidentally tries to construct it directly.

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Heinz Kabutz Java Conference Speaker

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