The Decorator Pattern

The Decorator Pattern
An Introduction with Examples in Java

Computer Science Department

bernstdh@jmu.edu

Motivation

Adding Capabilities to a Class:
- Specialization
Adding Capabilities to an Object:
- Needs to be done "dynamically" (i.e., at run time)

Examples of Use

A Model of the Decorator Pattern

An Example

An Example (cont.)

javaexamples/decorator/Printer.java

An Example (cont.)

javaexamples/decorator/ConsolePrinter.java

An Example (cont.)

javaexamples/decorator/PrinterDecorator.java

An Example (cont.)

javaexamples/decorator/UppercasePrinter.java

An Example (cont.)

javaexamples/decorator/WrappingPrinter.java

An Example (cont.)

javaexamples/decorator/Driver.java

An Alternative Implementation

The Issue:
- You need to decorate a class that does not implement an explicit interface
The Resolution:
- Specialize the class to be decorated but still use delegation

An Alternative Implementation (cont.)

An Example

There's Always More to Learn