33 lines
1.4 KiB
Markdown
33 lines
1.4 KiB
Markdown
---
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layout: pattern
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title: Null Object
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folder: null-object
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permalink: /patterns/null-object/
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categories: Behavioral
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tags:
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- Extensibility
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---
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## Intent
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In most object-oriented languages, such as Java or C#, references
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may be null. These references need to be checked to ensure they are not null
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before invoking any methods, because methods typically cannot be invoked on
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null references. Instead of using a null reference to convey absence of an
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object (for instance, a non-existent customer), one uses an object which
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implements the expected interface, but whose method body is empty. The
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advantage of this approach over a working default implementation is that a Null
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Object is very predictable and has no side effects: it does nothing.
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## Class diagram
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## Applicability
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Use the Null Object pattern when
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* You want to avoid explicit null checks and keep the algorithm elegant and easy to read.
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## Credits
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* [Pattern Languages of Program Design 3](https://www.amazon.com/gp/product/0201310112/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0201310112&linkCode=as2&tag=javadesignpat-20&linkId=7372ffb8a4e39a3bb10f199b89aef921)
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* [Refactoring to Patterns](https://www.amazon.com/gp/product/0321213351/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0321213351&linkCode=as2&tag=javadesignpat-20&linkId=2a76fcb387234bc71b1c61150b3cc3a7)
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