I am studying XML and Java and I see that both SAX&DOM are now part of standard Java (JAXP). But JDOM is not. At a glance, I notice that the functionalities of Sax, DOM & JDOM are quite the same. So what are the differences between JDOM and JAXP? Should I ignore JDOM?
JDOM (just like other APIs like XOM and dom4j) sits on top of SAX and/or DOM. So there's nothing it can do that you can't do with just SAX/DOM. If you're happy using the DOM API, by all means, ignore those other libraries. But the reason they came about is because people didn't think too highly of DOM and were looking for a better API. The other libraries also have the advantage of being Java-centric, whereas DOM is a cross-language API; so it doesn't feel very Java-ish to use. I'm a fan of XOM, but I'd advise to check out all of them with a few sample programs, and then to use the one you most like.
JODM supports both SAX and DOM methodology of XML parsing, So I suggest learn basics of this two methods and if you want to use the simplest implementation of this, go for JDOM library