Dr. Dobb's Journal - November 2007 - (Page 54)

d11jiri_p8db 9/13/07 12:54 PM Page 54 State of the Art REUSABLE ASSOCIATIONS There is more to UML than just the UML class diagrams though, and the new paradigm would also have to cover those other areas to provide the same utility as all of UML. The commonly used practice today is to add individual methods to classes where the implementation of the method is easiest or seems natural: void SourceXtoX:: add(Terminal *t,Net *n); void LinkXtoX::remove(); // USING THE METHODS Block *b; Terminal *t; Net *n; b->blockNets.add(t,n); t->blockNets.remove(); A Matter of Control Most associations need an iterator class, and these iterators can be implemented in the same style as collection iterators. However, when implementing associations, reusable or not, the question is where to keep the methods, which operate on the association. The second possibility is to select one class, preferably the “main” or “most important” class of the association, and keep all the methods in it. In the case of ManyToMany, there isn’t any clear difference between the Source and Target, which mirror each other. Let’s choose the Source: void SourceXtoX:: add(Terminal *t,Net *n); void SourceXtoX:: remove(Target *t); // USING THE METHODS Block *b; Terminal *t; Net *n; b->blockNets.add(t,n); b->blockNets.remove(t); This may look elegant, but it adds to the problem of having parts of the associations scattered throughout the classes and no guidance on where to find them. This interface is similar to the interface we use for collections today. Alternatively, for each association, we introduce a new class just to keep the association methods (Listing Three, available online; see “Resource Center,” page 5). This association control class (ACC) is a completely different concept from the UML association class (UAC) commonly used today. ACC provides the interface for the association, while UAC represents the data or state associated with the association. Note the paradigm shift. The user interface commonly used today: b->termByBlock.add(t,n); reads “for Block b and the collection termByBlock on it, add a link that connects it (meaning b) through t to n,” with emphasis on b. The new centralized control has a different order of parameters: blockNets::add(b,t,n); reads “for association blockNets, add a link from b through t to n,” with emphasis on the association. Data Hiding If we use centralized control, only the control class needs access to the inserted data. In C++, this can be easily arranged by adding friend statements: class Net { friend class nets; friend class blockNets; ChildAggregate nets; TargetXtoX blockNets; }; 54 Dr. Dobb’s Journal l www.ddj.com l November 2007 http://www.leadtools.com http://www.leadtools.com http://www.leadtools.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - November 2007

Contents Hmmmm Alia Vox Developer Diaries Developer’s Notebook Smart Compilers - But Smart Enough? Conversations Grid-Enabling Resource-Intensive Applications Distributed Computing: Windows and Linux Adobe AIR: Desktop/Web Convergence Transparency on Demand Reusable Associations Effective Concurrency The Agile Edge Swaine’s Flames

Dr. Dobb's Journal - November 2007

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