layout	title	folder	permalink	categories	tags
pattern	Decorator	decorator	/patterns/decorator/	Structural	Java Gang Of Four Difficulty-Beginner

Also known as

Wrapper

Intent

Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

Applicability

Use Decorator

• to add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects
• for responsibilities that can be withdrawn
• 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

Real World examples

• java.io.InputStream, java.io.OutputStream, java.io.Reader and java.io.Writer
• java.util.Collections#synchronizedXXX()
• java.util.Collections#unmodifiableXXX()
• java.util.Collections#checkedXXX()

Credits

• Design Patterns: Elements of Reusable Object-Oriented Software
• Functional Programming in Java: Harnessing the Power of Java 8 Lambda Expressions
• J2EE Design Patterns