如何将变量值从一类传递到另一类

Question

I have two packages one is com.firstBooks.series.db.parser which have a java file XMLParser.java, I have another package com.firstBooks.series79 which have a class called AppMain.NW I want to send the value of a variable called _xmlFileName frm AppMain class to the xmlFile variable in XMLParser class, I am posting the code for both the class, kindly help me.

package com.firstBooks.series.db.parser;

import java.io.IOException;
import java.io.InputStream;
import java.util.Vector;

import net.rim.device.api.xml.parsers.DocumentBuilder;
import net.rim.device.api.xml.parsers.DocumentBuilderFactory;
import net.rim.device.api.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

import com.firstBooks.series.db.Question;

public class XMLParser {

 private Document document;
 public static Vector questionList;
 public static String xmlFile;

 public XMLParser() {     
  questionList = new Vector();
 }


 public void parseXMl() throws SAXException, IOException,
   ParserConfigurationException {

  // Build a document based on the XML file.
  DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
  DocumentBuilder builder = factory.newDocumentBuilder();
  InputStream inputStream = getClass().getResourceAsStream(xmlFile);

  document = builder.parse(inputStream);
 }

 public void parseDocument() {
  Element element = document.getDocumentElement();

  NodeList nl = element.getElementsByTagName("question");

  if (nl != null && nl.getLength() > 0) {
   for (int i = 0; i < nl.getLength(); i++) {
    Element ele = (Element) nl.item(i);
    Question question = getQuestions(ele);
    questionList.addElement(question);
   }
  }
 }

 private Question getQuestions(Element element) {

  String title = getTextValue(element, "title");
  String choice1 = getTextValue(element, "choice1");
  String choice2 = getTextValue(element, "choice2");
  String choice3 = getTextValue(element, "choice3");
  String choice4 = getTextValue(element, "choice4");
  String answer = getTextValue(element, "answer");
  String rationale = getTextValue(element, "rationale");

  Question Questions = new Question(title, choice1,
    choice2, choice3, choice4, answer, rationale);

  return Questions;
 }

 private String getTextValue(Element ele, String tagName) {
  String textVal = null;
  NodeList nl = ele.getElementsByTagName(tagName);
  if (nl != null && nl.getLength() > 0) {
   Element el = (Element) nl.item(0);
   textVal = el.getFirstChild().getNodeValue();
  }

  return textVal;
 }
}

Nw the code for AppMain class

//#preprocess
package com.firstBooks.series79;

import net.rim.device.api.ui.UiApplication;

import com.firstBooks.series.ui.screens.HomeScreen;

public class AppMain extends UiApplication {

 public static String _xmlFileName; 
 public static boolean _Lite; 
 public static int _totalNumofQuestions;

 public static void initialize(){
   //#ifndef FULL  
     /* 
     //#endif 
        _xmlFileName = "/res/Series79_FULL.xml";
        _totalNumofQuestions = 50;
        _Lite = false;
     //#ifndef FULL 
     */  
  //#endif 

  //#ifndef LITE  
     /* 
     //#endif 
       _xmlFileName = "/res/Series79_LITE.xml";
       _totalNumofQuestions = 10;
       _Lite = true;
     //#ifndef LITE 
     */  
   //#endif 
  }


 private AppMain() {
  initialize();
  pushScreen(new HomeScreen());
 }

 public static void main(String args[]) {
  new AppMain().enterEventDispatcher();
 }
}

Answer 1

You just have to type:

 XMLParser.xmlFile = AppMain._xmlFileName;

For instance here:

public static void main(String args[]) {
  new AppMain().enterEventDispatcher();
  XMLParser.xmlFile = AppMain._xmlFileName;
}

I'm not sure if that's the best design, but address your question.

Answer 2

Well, the way you have it set up, one line:

XmlParser.xmlFile = _xmlFileName;

in your AppMain somewhere, say the initialize method, should do the trick. Maybe I'm not understanding your question. It seems likely that you wouldn't want xmlFile to be a public static, but that's your choice.

Answer 3

Other answers are correct, but using static variables like that is a rather rigid design. It will cause problems if you later want to use a second XMLParser object to parse a different file.

Instead, the XMLParser constructor could take the file name as a parameter:

public class XMLParser {

  private Document document;
  public static Vector questionList;
  private static String xmlFile;  // this can be private

  public XMLParser(String xmlFile) {
    this.xmlFile = xmlFile;
    questionList = new Vector();
  }

Then in some other part of the application, when you create the XMLParser:

XMLParser xmlParser = new XMLParser(AppMain._xmlFileName);