The JUnit-Wrapper classes are pure stubs that delegate all work to XLT's script interpreter which parses and executes the commands contained in the XML file (the test script). These wrapper classes are overwritten each time you save your script in Script Developer; thus any modification you make there will get lost upon save.
According to your code snippets I assume that you want to code the tests by yourself, or customize them at least. So, you will need to export your tests to Java using XLT's Scripting API.
Then, you can simply do
All commands that you can use in Script Developer can also be used in XLT's Scripting API. And each command that interacts with elements support element locators. Per default, elements are located by ID-or-XPath which means that the passed string is interpreted as ID first and in case no element was found, it is interpreted as XPath.