Speculative Generality
Signs and Symptoms
There's an unused class, method, field or parameter.
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Reasons for the Problem
Sometimes code is created "just in case" to support anticipated future features that never get implemented. As a result, code becomes hard to understand and support.
Treatment
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For removing unused abstract classes, try Collapse Hierarchy.
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Unnecessary delegation of functionality to another class can be eliminated via Inline Class.
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Unused methods? Use Inline Method to get rid of them.
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Methods with unused parameters should be given a look with the help of Remove Parameter.
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Unused fields can be simply deleted.
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Payoff
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Slimmer code.
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Easier support.
When to Ignore
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If you're working on a framework, it's eminently reasonable to create functionality not used in the framework itself, as long as the functionality is needed by the frameworks's users.
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Before deleting elements, make sure that they aren't used in unit tests. This happens if tests need a way to get certain internal information from a class or perform special testing-related actions.