Design Patterns | Decorator

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1. References
2. Example
   • The Component
   • The Concrete Component
   • The Decorator
   • The Concrete Decorator
   • A simple class to test the Decorator design pattern

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1. References
   • Definition: (source: http://en.wikipedia.org/wiki/Decorator_pattern)
     
     The decorator pattern can be used to extend (decorate) the functionality of a certain object statically, or in some cases at run-time, independently of other instances of the same class, provided some groundwork is done at design time.
     
     
   • Class diagram: (source: http://en.wikipedia.org/wiki/Decorator_pattern)
     
     
2. Example
   • The Component:
     
     public interface Logger { void log(); }
     
   • The Concrete Component:
     
     public class FileLogger implements Logger { public void log() { System.out.println("FileLogger-log"); } }
     
   • The Decorator:
     
     public abstract class CustomLogger implements Logger { private final Logger logger = new FileLogger(); public void log() { logger.log(); } }
     
   • The Concrete Decorator:
     
     public class AuditLogger extends CustomLogger { public void log() { super.log(); System.out.println("AuditLogger-log"); } }
     
   • A simple class to test the Decorator design pattern:
     
     public class DecoratorPatternTest { public static void main(String[] args) { // create the decorator final Logger logger = new AuditLogger(); // call the decorated method logger.log(); } }