This interface defines the invocation API for user-defined XPath functions. Arguments are passed to the evaluate( ) method as a java.util.List and the return value should be an Object. evaluate( ) may throw an XPathFunctionException. See also XPathFunctionResolver.

public interface XPathFunction {
// Public Instance Methods
     Object evaluate(java.util.List args) throws XPathFunctionException;  
}

Returned By

XPathFunctionResolver.resolveFunction( )