[JXPath] Compiled expression with var before vars are declared

[Psi Aushilfe3]

Hi!

public class Blah
{
        final static CompiledExpression c =
JXPathContext.compile("whatever[blah=$var]");

        public void init(JXPathContext xpath)
        {
                xpath.getVariables().declareVariable("var", something);
        }
}

Is this valid? Can I compile the expression before I actually declare
the variable?