Parse XML by ID in Java

I'm trying to parse a XML-File by ID. But I always get a NullPointerExeption.

My XML looks like this:

<root>
    <default>
        <area>
            <param id="hello">Hello</param>
            <param id="hey">Hey</param>
        </area>
  </default>
</root>

My Java code:

try {
String text;
File xmlFile= new File("C:\\Users\\Public\\Desktop\\test.xml");
DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(xmlFile);

text = doc.getElementById("hello").getTextContent(); // NullPointer
System.out.println(text);
} catch (Exception e){
    e.printStackTrace();
}

I get the NullPointer at this line:

text = doc.getElementById("hello").getTextContent();

I debuged it. The Object doc isn't null. So I think it can't find the id "hello".

Thanks for helping!