CIS501 Exercise: Factory Methods

Download and unzip Lec11FM.zip.  Study the class diagram, which shows how to use the FM pattern for reading/writing files.   

Notice that methods  closeRead  and  closeWrite  are *private*.  Notice the delegate,  CloseOp. 

Open the VS Solution ReaderWriter.  Read the code for the factory methods,  openRead  and  openWrite,  to see how the delegate is used.

Now rebuild and demo the code:  Write some lines to the file, close, and then try to make both RThreads read the file at the same time --- it doesn't work!

Repair  class FileController  so that both  RThread  objects can read the file at the same time.



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RECAP of Thursday's exercise with factory methods:

When a  RThread  reads the lines of the file, it uses its own  FileReader  object, constructed by the factory method,   public FileReader makeReader(CloseOp c);

Parameter  c  is bound to a delegate (method) holding "clean-up" code that must execute when the FileReader is told to  close().  The protocol goes:
   1.  RThread  asks  FileController  to  openRead() and receives in return a handle to a  FileReader.
   2.  RThread  repeatedly asks its  FileReader  to  read().
   3.  When finished,  RThread  tells its  FileReader to  close().  The latter executes a call to  FileController.closeRead() via the delegate.