According to spec , evaluate() should throw NPE if expression or returnType is null
XPath.evaluate(java.lang.String expression, java.net.URL documentURL)
XPath.evaluate(java.lang.String expression, java.net.URL documentURL, QName returnType)

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java -version
java version "1.5.0-beta2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta2-b37)
Java HotSpot(TM) Client VM (build 1.5.0-beta2-b37, mixed mode)

javac Test8.java
java Test8
 checkXPath41() - failed : expecting NPE , but XPathExpressionException thrown
 checkXPath46() - failed : expecting NPE , but XPathExpressionException thrown
 checkXPath47() - failed : expecting NPE , but XPathExpressionException thrown

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Testcase - Test8.java & sample xml - widgets.xml attached
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<?xml version="1.0" standalone="yes"?>
<widgets>
<widget name="a" style="red" quantity="6"/>
<widget name="b" style="blue"/>
<widget name="c">
<style>green</style>
</widget>
</widgets>

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// checkXPath41()
// checkXPath46()
// evaluate() should throw NPE when expression or returnType is null

/*
According to spec , evaluate() should throw NPE if expression or returnType is null
XPath.evaluate(java.lang.String expression, java.net.URL documentURL)
XPath.evaluate(java.lang.String expression, java.net.URL documentURL, QName returnType)
*/

import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathFactory;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathFactoryConfigurationException;
import javax.xml.xpath.XPathExpressionException;

import java.net.URL;

public class Test8 {
   
   URL url = null;
   Test8 () { }
   
    // main()
    public static void main(String[] argv) {
        Test8 xpath01 = new Test8();
        xpath01.init();
        xpath01.checkXPath41();
        xpath01.checkXPath46();
        xpath01.checkXPath47();
    }
    
        // initializing
    private void init(){
        try {
            url = new URL("http://sqindia.india.sun.com/disk06/tea/sreejith/jaxp/widgets.xml");
        }catch (Exception e) {
          System.out.println(" Exception thrown in XPath01/init() - Test failed");
        }
    }


    // test for XPath.evaluate(java.lang.String expression, java.net.URL documentURL)
    // expression is null , should throw NPE
    private void checkXPath41() {
     try{
     XPathFactory xpathFactory = XPathFactory.newInstance();
     if( xpathFactory instanceof XPathFactory ){
     XPath xpath = xpathFactory.newXPath();
if ( xpath instanceof XPath ){
String expression = null;
String quantity = (String) xpath.evaluate(expression, url);
System.out.println("checkXPath41() : failed - expected NPE not thrown");

}
     else{
     System.out.println("checkXPath41() failed - xpath not instance of XPath");
     }
     }else{
     System.out.println(" checkXPath41() failed - creating instance of XPathFactory ");
     }
     }catch(NullPointerException npe ){
     System.out.println(" checkXPath41() - passed , expected NPE thrown ");
     }catch(XPathFactoryConfigurationException xpfce ){
     System.out.println(" checkXPath41() - failed , Default object model not available ");
     }catch(XPathExpressionException xpee ){
     System.out.println(" checkXPath41() - failed : expecting NPE , but XPathExpressionException thrown ");
     }catch(Exception e){
     System.out.println(" Exception thrown - checkXPath41() failed ");
     }
    }


    // test for XPath.evaluate(java.lang.String expression, java.net.URL documentURL, QName returnType)
    // expression is null , should throw NPE
    private void checkXPath46() {
     try{
     XPathFactory xpathFactory = XPathFactory.newInstance();
     if( xpathFactory instanceof XPathFactory ){
     XPath xpath = xpathFactory.newXPath();
if ( xpath instanceof XPath ){
String expression = null;
String quantity = (String) xpath.evaluate(expression, url, XPathConstants.STRING);
System.out.println("checkXPath46() : failed - expected NPE not thrown" );

}
     else{
     System.out.println("checkXPath46() failed - xpath not instance of XPath");
     }
     }else{
     System.out.println(" checkXPath46() failed - creating instance of XPathFactory ");
     }
     }catch(NullPointerException npe ){
     System.out.println(" checkXPath46() - passed , expected NPE thrown ");
     }catch(XPathFactoryConfigurationException xpfce ){
     System.out.println(" checkXPath46() - failed , Default object model not available ");
     }catch(XPathExpressionException xpee ){
     System.out.println(" checkXPath46() - failed : expecting NPE , but XPathExpressionException thrown ");
     }catch(Exception e){
     System.out.println(" Exception thrown - checkXPath46() failed ");
     }
    }
    
    // test for XPath.evaluate(java.lang.String expression, java.net.URL documentURL, QName returnType)
    // returnType is null , should throw NPE
    private void checkXPath47() {
     try{
    
     XPathFactory xpathFactory = XPathFactory.newInstance();
     if( xpathFactory instanceof XPathFactory ){
     XPath xpath = xpathFactory.newXPath();
if ( xpath instanceof XPath ){
String expression = "/widgets/widget[@name='a']/@quantity";
String quantity = (String) xpath.evaluate(expression, url, null);
System.out.println("checkXPath47() : failed - expected NPE not thrown" );

}
     else{
     System.out.println("checkXPath47() failed - xpath not instance of XPath");
     }
     }else{
     System.out.println(" checkXPath47() failed - creating instance of XPathFactory ");
     }
     }catch(NullPointerException npe ){
     System.out.println(" checkXPath47() - passed , expected NPE thrown ");
     }catch(XPathFactoryConfigurationException xpfce ){
     System.out.println(" checkXPath47() - failed , Default object model not available ");
     }catch(XPathExpressionException xpee ){
     System.out.println(" checkXPath47() - failed : expecting NPE , but XPathExpressionException thrown ");
     }catch(Exception e){
     System.out.println(" Exception thrown - checkXPath47() failed ");
     }
    }
    

}
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