AreDTD, XLT, XSL sheets required when using XML in Java

I have been reading some tutorials about using XML in Java and using Document Type Definition, XML schemas or XSL to defin the XML files you use.

From my reading it seemdd that one of these were needed whenever you using XML files with Java. However recently I have been studying some Java application code (sometimes with quite extensiec and complex use of XML) but I have not found any of these type of files with the application.

Can someone comment on if these type of files (DTD, XLT, XSL) are always necesary or when they would or wouldn't be required?

[578 byte] By [voodoo31a] at [2007-11-26 18:52:00]