Design Patterns - Decorator

Design Patterns | Decorator

References
Example

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)

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();
    }
}