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[aspectj-users] A Pattern Implementation
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Hi,
I am reading this paper
"Implementing Design Patterns Using Advanced Separation of Concerns"
written by Noda and Kishi, published in a workshop on ASOC in OOS - OOPSLA 01.
It implements GoF Observer pattern using AspectJ. For each of the two pattern roles i.e. Subject and Observer, authors define two aspects - one reusable and other for binding this reusable part to classes in a particular context. Part of their implementation is shown below:
public abstract aspect Subject {
protected Vector observers = new Vector();
public void attach( Observer obs ) {
...
}
}
public aspect CounterAsSubject extends Subject of eachobject( instanceof(Counter) ) {
...
}
Usually we need to inherit context classes from pattern roles to implement design patterns. Here, I cannot understand how the context or application classes can use the abstractions of pattern roles i.e. how class Counter implementing Subject role can register an observer object? Perhaps I need an explanation of the phrase "of eachobject( instanceof(Counter) )".
A lot of thanks in advance.
Regards,
Aamir Raheem,
NUCES,
Pakistan.
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