| = Composite Pattern |
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| The http://en.wikipedia.org/wiki/Composite_pattern[Composite Pattern] allows you to treat single instances of an object the same way as a group of objects. The pattern is often used with hierarchies of objects. Typically, one or more methods should be callable in the same way for either __leaf__ or __composite__ nodes within the hierarchy. In such a case, composite nodes typically invoke the same named method for each of their children nodes. |
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| == Example |
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| Consider this usage of the composite pattern where we want to call ++toString()++ on either ++Leaf++ or ++Composite++ objects. |
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| image::assets/img/CompositeClasses.gif[] |
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| In Java, the ++Component++ class is essential as it provides the type used for both leaf and composite nodes. In Groovy, because of duck-typing, we don't need it for that purpose, however, it can still server as a useful place to place common behaviour between the leaf and composite nodes. |
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| For our purposes, we will assemble the following hierarchy of components. |
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| image::assets/img/CompositeComponents.gif[] |
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| Here is the code: |
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| [source,groovy] |
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| include::{projectdir}/src/spec/test/DesignPatternsTest.groovy[tags=composite_code,indent=0] |
| ---- |
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| Here is the resulting output: |
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| ---- |
| root |
| -leaf A |
| -comp B |
| --leaf B1 |
| --leaf B2 |
| -leaf C |
| ---- |
