Programmatically Change the styleClass of a Web page element

Question

Somehow this should be very simple. But being new to jsp, I am unfamiliar with how to do this. Lets say I have some element on a page that looks like this:
<div id="testElement" class="class1">test text</div>
I have class1 and class2 defined in my jsp page style section
How do I reference the testElement item in order to change the styleClass.
I tried using something like this:
<%
testElement.setStyleClass("testClass2");
%>
I realize I am missing something very basic here. Any help is much appreciated.

Answer 1

You are mixing up java/jsp with javascript.
These two things are not the same, even if they have similar names.
Java/JSP runs on the server, and produces an HTML page.
Javascript runs on the client (inside the browser) and handles button clicks/dynamic changing of the page.
In this case you are wanting to use javascript.
I think it would be something like
<script>
testElement.className = 'testClass2';
</script>
<style>
  .redText  {color: red;}
  .blueText {color: blue;}
</style>
<div id="testElement" class="redText">  This is an example</div>
<button onclick="testElement.className='redText'">Red</button>
<button onclick="testElement.className='blueText'">blue</button>