XPath result while evaluating with XPathConstants.BOOLEAN

Question

I am trying to get the value of a boolean attribute but I am getting the wrong result when I try using XPathConstants.BOOLEAN.
When I use XPathConstants.STRING I do get the correct value.
The following code:
public static void main(String[] args) throws Exception {
          String xml = "<?xml version=\"1.0\" ?>" +
                    "<root check=\"false\" />";
          InputSource inputSource = new InputSource(new StringReader(xml));
          Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(inputSource);
          XPath xPath = XPathFactory.newInstance().newXPath();
          System.out.println("check as string: " + xPath.evaluate("root/@check", document, XPathConstants.STRING));
          System.out.println("check as boolean: " + xPath.evaluate("root/@check", document, XPathConstants.BOOLEAN));
     }Has the following output:
check as string: false
check as boolean: true
Please explain.

Answer 1

I'm guessing (because I can't find any specific documentation on what that constant means) that it evaluates the XPath expression and then coerces it to a boolean value. I'm also guessing that it uses the XPath boolean() function to do that. And you can read about what the boolean() function does here: [http://www.w3.org/TR/xpath#section-Boolean-Functions]