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The most obvious difference in speed was recursive traversal of dom elements in Javascript, which is always a lot faster than the same method implemented in Java.

Why is this the case? Why am I able to traverse dom document much quicker than Java, especially when they share the identical method (recursion).

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    The browser implements DOM at its core, in highly optimized native code. Java implements DOM in Java... Commented Oct 16, 2011 at 22:49
  • @nos org.w3c.dom, then I wrote the same recursive traversal from my Javascript implementation in Java. JS is much faster even after optimizing the Java implementation. Commented Oct 16, 2011 at 22:53
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    "Why is it faster to access DOM document via Javascript than Java?" [citation-needed] Commented Oct 16, 2011 at 22:58

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It's because browsers do not have interpreters for java. They interpret javascript. The DOM is a model that can be used anywhere, but it used mostly in the browser environment, and browsers have optimized DOM parsing over the years... for javascript.

The reason browsers have optimized DOM parsing is due to the fact that DOM parsing is a cornerstone of dynamic web development. Consider the normal way to make a page more dynamic:

1.) Listen for some events fired on the page.
2.) When those events are fired, modify some number of DOM objects, 
    e.g., by changing their visibility, geometry, or actually moving
    them to other portions of the DOM.

The reason the DOM is important here is because it provides a specification for storing a document in browser memory so that an entire page doesn't have to be re-rendered by changes to small portions of the markup. And these DOM objects stored in browser memory are structured just like native javascript objects; therefore, it's easier to optimize for javascript against them.

And ever since dynamic web pages have become essential, browsers have been fighting each other tooth and nail to have the fastest custom javascript interpreter, and in a dynamic web environment, the main place where you're going to be able to see the most rewards for optimizing is DOM parsing.

I can't see the pressing need in a java environment to use a DOM, but it's absolutely essential in a browser environment. That is the most likely reason you have seen better optimizations in javascript for DOM parsing than java. More people have a vested interest in making it work in the browser. However, for clarification, I'm not sure of the exact technical reasons at the code level why it's actually faster.

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Err, browsers do have interpreters for Java, it's called the JVM or Java plugin. This answer doesn't explain anything.
The answer was meant to point out that browsers don't treat java as first-class citizens... and thus, they don't optimize DOM parsing for java. And the JVM is a generic interpreter for java, it's not a browser-specific interpreter. Whereas, browser vendors go to great lengths to write custom interpreters for javascript.
Browsers don't do anything about DOM parsing for Java. Java does, and as a matter of fact in a highly optimized way.
The DOM is a first-class citizen in the browser environment. And as a result, the browsers are highly optimized to handle DOM parsing. And the language that takes advantage of this, in the browser, is javascript. To add to that matter, java hasn't had as much of a need to do DOM parsing as browsers, and thus, it probably hasn't been as highly optimized in java as it has been in browsers.
Exactly. It has nothing to do with whether or not browsers do or don't have interpreters for Java. Fix your answer for upvote.
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I think the answer can be summarised with "Because that's the kind of access that the browser developers have put more effort into."

If, in an alternate universe, everybody used Java to provide rich interactivity on web pages and Javascript was only used for annoying scrolling banner bars, then you might very well be asking the opposite question. In such a universe, the browser vendors would have made DOM access from Java as fast as possible.

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Your Java code is probaby using a general-purpose XML parser such as Xerces, with error correction taking place for the non-XML-compliant parts of HTML. Your Javascript is probably using a highly-optimized HTML-specific parser whose CPU-intensive portion is almost certainly implemented in native code.

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