Singletonizer
From APIDesign
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[[Singletonizer]] is a simplification of [[Factory]] by use of [[Generics]]. It is very useful pattern for creating [[ProviderAPI]]. On the other hand, it is not that useful for [[ClientAPI]], as its use requires an [[OpenClass]] concept. | [[Singletonizer]] is a simplification of [[Factory]] by use of [[Generics]]. It is very useful pattern for creating [[ProviderAPI]]. On the other hand, it is not that useful for [[ClientAPI]], as its use requires an [[OpenClass]] concept. | ||
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| + | == Real Example == | ||
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| + | [[Graal]] '''Graph I/O''' [[API]] is using the [[singletonizer]] pattern in its [http://www.graalvm.org/graphio/javadoc/org/graalvm/graphio/package-summary.html javadoc]. | ||
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| + | == Artificial Sample == | ||
Instead of having one class representing a [[Factory]] which creates another class representing the ''data'', one can move all the methods into one class: | Instead of having one class representing a [[Factory]] which creates another class representing the ''data'', one can move all the methods into one class: | ||
Revision as of 06:49, 25 January 2018
Singletonizer is a simplification of Factory by use of Generics. It is very useful pattern for creating ProviderAPI. On the other hand, it is not that useful for ClientAPI, as its use requires an OpenClass concept.
Real Example
Graal Graph I/O API is using the singletonizer pattern in its javadoc.
Artificial Sample
Instead of having one class representing a Factory which creates another class representing the data, one can move all the methods into one class:
does not exists: day.end.bridges.Digestor
This simplifies the life for the implementors of the Digestor class while retaining the same power as they had before. They have to subclass and implement just one type. Yet they can also have own data type. Moreover, due to use of Generics they do not need to deal with any casts or unsafe type checking. Or, just like in following example, one can reuse suitable existing data type:
does not exists: day.end.bridges.CountingDigestor
Singletonizer is useful when representing complex graphs or tree hierarchies. One can have a class in a ClientAPI that represents each graph's vertex. There can be tons of its instances. Yet plugging in behaviour for each instance can be quite simple. They can all delegate to single Singletonizer implementation which handles all their operation. Thus they are basically singletonizing behaviour of many instances to one - hence the name Singletonizer:
does not exists: day.end.bridges.DigestImpl
Btw. the DigestImpl's ACCESSOR field, which slightly complicates the code, is an example of friend accessor pattern allowing us to access protected methods of Digestor class located in different package.
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