XMidi Changes for Version 1.4

Changes in the last version (1.2) can be found here. The changes for version 1.4 are these:

• The DOM approach to parsing has been replaced by SAX. This makes the program faster, and capable of handling larger files.
• No more "plug-in" parsers. The early version was written before javax.xml.parsers was a part of the JDK and I wanted to be sure that my code was not tied to any one parser. I think I handled that particular problem very well. However, now the javax.xml.parsers is part of the JDK, I see no reason not to use it. Particularly, when it allows for at least two kinds of plug-ins.
• Since the structure of the XMidi files corresponds very closely with the structure of MIDI files, I was able to use the "state" pattern to handle tags in XM and MIDI events in MX. The base class for all the tag classes is Tag and there is a subclass for each different element in the DTD. These classes have methods which are invoked from XM in the SAX methods (startElement, endElement, and characters) and they have methods which are invoked from the appropriate places in MX (createStartXML and createEndXML). There is a State class, which is little more than a collection of variables to be passed around to various methods. This allows objects and methods to interact using the variables they were expecting.
• The old version of MX created a DOM tree as it was reading the input, then traversed the tree and wrote the output. This has been replaced by writing the output as the input is being read using the createStartXML and createEndXML methods of the various Tag subclasses. This is faster and allows larger files to be handled.
• The prior version was not "thread safe". This one is. This has been accomplished by removing static (class) variables (except for constants).