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Ilkka Seppälä
2024-06-08 19:54:44 +03:00
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decorator/README.md
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@@ -1,13 +1,15 @@
---
title: Decorator
title: "Decorator Pattern in Java: Extending Classes Dynamically"
shortTitle: Decorator
description: "Learn how the Decorator Design Pattern enhances flexibility in Java programming by allowing dynamic addition of responsibilities to objects without modifying their existing code. Explore real-world examples and implementation."
category: Structural
language: en
tag:
- Enhancement
- Extensibility
- Gang of Four
- Object composition
- Wrapping
- Enhancement
- Extensibility
- Gang of Four
- Object composition
- Wrapping
---
## Also known as
@@ -15,11 +17,11 @@ tag:
* Smart Proxy
* Wrapper
## Intent
## Intent of Decorator Design Pattern
The Decorator pattern allows for the dynamic addition of responsibilities to objects without modifying their existing code. It achieves this by providing a way to "wrap" objects within objects of similar interface.
The Decorator pattern allows for the dynamic addition of responsibilities to objects without modifying their existing code. It achieves this by providing a way to "wrap" objects within objects of similar interface, enhancing Java design patterns flexibility.
## Explanation
## Detailed Explanation of Decorator Pattern with Real-World Examples
Real-world example
@@ -33,7 +35,7 @@ Wikipedia says
> In object-oriented programming, the decorator pattern is a design pattern that allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class. The decorator pattern is often useful for adhering to the Single Responsibility Principle, as it allows functionality to be divided between classes with unique areas of concern as well as to the Open-Closed Principle, by allowing the functionality of a class to be extended without being modified.
**Programmatic Example**
## Programmatic Example of Decorator Pattern in Java
There is an angry troll living in the nearby hills. Usually, it goes bare-handed, but sometimes it has a weapon. To arm the troll it's not necessary to create a new troll but to decorate it dynamically with a suitable weapon.
@@ -131,33 +133,33 @@ Program output:
11:34:18.101 [main] INFO com.iluwatar.decorator.App -- Clubbed troll power: 20.
```
## Applicability
## When to Use the Decorator Pattern in Java
Decorator is used to:
* Add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects.
* Add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects, a key feature of Java design patterns.
* For responsibilities that can be withdrawn.
* When extending a class is impractical due to the proliferation of subclasses that could result.
* For when a class definition might be hidden or otherwise unavailable for subclassing.
## Tutorials
## Decorator Pattern Java Tutorials
* [Decorator Design Pattern in Java Example (DigitalOcean)](https://www.digitalocean.com/community/tutorials/decorator-design-pattern-in-java-example)
## Known uses
## Real-World Applications of Decorator Pattern in Java
* GUI toolkits often use decorators to dynamically add behaviors like scrolling, borders, or layout management to components.
* [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), [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)
* The [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), [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) classes in Java are well-known examples utilizing the Decorator pattern.
* [java.util.Collections#synchronizedXXX()](http://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#synchronizedCollection-java.util.Collection-)
* [java.util.Collections#unmodifiableXXX()](http://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#unmodifiableCollection-java.util.Collection-)
* [java.util.Collections#checkedXXX()](http://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#checkedCollection-java.util.Collection-java.lang.Class-)
## Consequences
## Benefits and Trade-offs of Decorator Pattern
Benefits:
* Greater flexibility than static inheritance.
* Avoids feature-laden classes high up in the hierarchy.
* Avoids feature-laden classes high up in the hierarchy, showcasing the power of Java design patterns.
* A decorator and its component aren't identical.
* Responsibilities can be added or removed at runtime.
@@ -167,13 +169,13 @@ Trade-offs:
* Decorators can lead to a system with lots of small objects that look alike to the programmer, making the desired configuration hard to achieve.
* Overuse can complicate the code structure due to the introduction of numerous small classes.
## Related Patterns
## Related Java Design Patterns
* [Adapter](https://java-design-patterns.com/patterns/adapter/): A decorator changes an object's responsibilities, while an adapter changes an object's interface.
* [Composite](https://java-design-patterns.com/patterns/composite/): Decorators can be viewed as a degenerate composite with only one component. However, a decorator adds additional responsibilities—it isn't intended for object aggregation.
* [Strategy](https://java-design-patterns.com/patterns/strategy/): Decorator lets you change the skin of an object, while Strategy lets you change the guts.
## Credits
## References and Credits
* [Design Patterns: Elements of Reusable Object-Oriented Software](https://amzn.to/3w0pvKI)
* [Functional Programming in Java](https://amzn.to/3JUIc5Q)