If u want to maintain tags  in a file,why don't u use xml file?If u use xml,u can
use parser(dom or sax  parser) to retrieve the details.If u use flat,it is very
difficult to retrieve the details.

Here is the coolest way I have found to manage config files (tags). Hope
this helps.

Sax or Jaxp are parsers.
they r not classes.
this text  file is called an XML file.
java has a full technology dedicated to handling XML.

for more inf see -

http://java.sun.com/xml/tutorial_intro.html

after u finish this link, go through

http://java.sun.com/xml/download.html

I have read the documentation about XML and I want to know if I have
understood well. I can create an xml file  from the scratch creating
a DOM and inserting in it the tags  and the text  I want. Then, I can
write out this DOM with a transformer.
This is how I create an XML file, doesn't it?

And then, if I want to recover the XML file data somewhow, I can
create a DOM again to operate with it, or reading it by SAX.Is it
correct?

And, another XML question :). If I have something like this:

<hdp>
bla bla bla
<has_solution>
ble ble ble
</has_solution>
</hdp>

is this extract well formed? I mean, the text "bla bla bla" is in a
correct way?