44 lines
2.3 KiB
Markdown
44 lines
2.3 KiB
Markdown
---
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layout: pattern
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title: Decorator
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folder: decorator
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permalink: /patterns/decorator/
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pumlid: HSV14SCm20J0Lk82BFxf1YF6LaP26ZZizfDVVhjRC-bPDRs_Bc35cyZvAMV3bKU6kao36ehCGQtdms2d3z-yLursshuOKBUWmV43LPNfZEcaaFzA-YWhH_y2
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categories: Structural
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tags:
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- Java
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- Gang Of Four
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- Difficulty-Beginner
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---
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## Also known as
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Wrapper
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## Intent
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Attach additional responsibilities to an object dynamically.
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Decorators provide a flexible alternative to subclassing for extending
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functionality.
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## Applicability
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Use Decorator
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* To add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects
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* For responsibilities that can be withdrawn
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* When extension by subclassing is impractical. Sometimes a large number of independent extensions are possible and would produce an explosion of subclasses to support every combination. Or a class definition may be hidden or otherwise unavailable for subclassing
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## Real world examples
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* [java.io.InputStream](http://docs.oracle.com/javase/8/docs/api/java/io/InputStream.html), [java.io.OutputStream](http://docs.oracle.com/javase/8/docs/api/java/io/OutputStream.html),
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[java.io.Reader](http://docs.oracle.com/javase/8/docs/api/java/io/Reader.html) and [java.io.Writer](http://docs.oracle.com/javase/8/docs/api/java/io/Writer.html)
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* [java.util.Collections#synchronizedXXX()](http://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#synchronizedCollection-java.util.Collection-)
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* [java.util.Collections#unmodifiableXXX()](http://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#unmodifiableCollection-java.util.Collection-)
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* [java.util.Collections#checkedXXX()](http://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#checkedCollection-java.util.Collection-java.lang.Class-)
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## Credits
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* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)
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* [Functional Programming in Java: Harnessing the Power of Java 8 Lambda Expressions](http://www.amazon.com/Functional-Programming-Java-Harnessing-Expressions/dp/1937785467/ref=sr_1_1)
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* [J2EE Design Patterns](http://www.amazon.com/J2EE-Design-Patterns-William-Crawford/dp/0596004273/ref=sr_1_2)
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