JAVA-将方法返回类型从void更改为String会立即创建“死”代码吗？

Question

I wrote a class a while back, which gets a specific set of values from specific XML files. It can then print the results in Console and it works just fine. But of course I didn't make a class to print to console

I need to get the values into a database. There is a separate class that handles the db input.

But I am having great trouble getting the local variables from the method that loops the XML files returned/passed to the database class.

I cannot get the values from inside the main method that reads them from the XML files (the values from the Nodelist 'nodes'). I tried using a bunch of global variables, but they don't get updated. I read that using 'global variables' was the way to go, but I also read (and found out when coding), that JAVA makes a copy from the actual bits inside the object and works with that inside a method. So when the method ends all the alterations made to variables are ignored and the value of the object is the same as it was before the method ran.

Here is the code that gives the problem:

import org.w3c.dom.*;
import javax.xml.xpath.*;
import javax.xml.parsers.*;
import java.io.IOException;
import org.xml.sax.SAXException;

public class xmlGrabber {
public static String NAME = "StartNaam"; // declare the global variable


  public String main(String[] args) 
   throws ParserConfigurationException, SAXException, 
          IOException, XPathExpressionException {

    DocumentBuilderFactory domFactory = 
    DocumentBuilderFactory.newInstance();
          domFactory.setNamespaceAware(true); 
    DocumentBuilder builder = domFactory.newDocumentBuilder();
    String docuInvoer = "C:/temp/document.xml";
    Document doc = builder.parse(docuInvoer);
    XPath xpath = XPathFactory.newInstance().newXPath();
       // XPath Query for showing all nodes value
    XPathExpression expr = xpath.compile("//@fieldvalue");

    Object result = expr.evaluate(doc, XPathConstants.NODESET);
    NodeList nodes = (NodeList) result;
    for (int i = 1; i < 24; i++) {
    // System.out.println(nodes.item(i).getNodeValue()); 
     //String bla = nodes.item(1).getNodeValue(); 
    String NAME = nodes.item(1).getNodeValue(); //Modify value of NAME

    } return NAME;
  }
//  public static String NAME(){
    //  System.out.println(NAME+"test");
    //  return NAME;        
    //  }
}

When trying to read the variable in a different class like so:

public class Debug {
 public static void main(String[] args) {
     xmlGrabber.main(null);
     String name = xmlGrabber.NAME;
     System.out.println(name); 
 }
}

The IDE throws the error: NAME cannot be resolved or is not a field

Answer 1

When the compiler checks for dead code, it makes an exception for a main method with the signature

public static void main(String[] args)

because the point of the main method is it is an entry point, something that you can call from the command line or from a script or something and kick things off.

When you change the return type then it doesn't match that signature, it's no longer a valid main method, just some method that nowhere else in the program calls: dead code.

Also, when your main method stops running the program goes away. For you to save the results of your xml parsing to a database either you should make calls from your xml parsing code to the data access class (alternatively you could write the results to stdout and pipe them to a separate java program that reads data from stdin and saves it to the database).

Answer 2

On this line you use 1 instead of i:

xmlGrabber.NAME = nodes.item(1).getNodeValue();

That probably explains the compiler warning and why printing to the console works but retrieving the nodes doesn't.