为什么实体名称必须紧跟在为XML出现的实体引用中的"&"后面？

我在eclipse中运行的代码如下:

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;


import org.apache.log4j.Logger;
import org.apache.log4j.xml.DOMConfigurator;
import org.openqa.selenium.By;
import org.openqa.selenium.JavascriptExecutor;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.interactions.Actions;
import org.openqa.selenium.support.ui.Select;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public class A {

    
    static Properties p= new Properties();
    String url=p.getProperty("url");
    private static Logger Log = Logger.getLogger(A.class.getName());

    public static void main(String[] args) throws SAXException, IOException, ParserConfigurationException, InterruptedException {
    	WebDriver driver = new FirefoxDriver();
        A a = new A();
      
    	Actions actiOns= new Actions(driver);
    	DOMConfigurator.configure("src/log4j.xml");
        String url = a.readXML("logindetails","url");
        String username = a.readXML("logindetails","username");
        String password = a.readXML("logindetails","password");
     
        //use username for webdriver specific actions
        Log.info("Sign in to the OneReports website");
        driver.manage().window().maximize();
        driver.get(url);
        Thread.sleep(5000);
        Log.info("Enter Username");
        driver.findElement(By.id("loginUsername")).sendKeys(username);
        Log.info("Enter Password");
        driver.findElement(By.id("loginPassword")).sendKeys(password); 
        //submit
        Log.info("Submitting login details");
        waitforElement(driver,120 , "//*[@id='submit']");
        driver.findElement(By.id("submit")).submit();
        Thread.sleep(5000);

    	 	Log.info("Clicking on Reports link");
	        String id_r = a.readXML("kpi","id_r");
	        WebElement menuHoverLink = driver.findElement(By.id(id_r));
 		   	actions.moveToElement(menuHoverLink).perform();
 		   	Thread.sleep(6000);
 		   
 		   String id_e = a.readXML("kpi","id_e");
 		   WebElement menuHoverLink1 = driver.findElement(By.id(id_e));
 		   actions.moveToElement(menuHoverLink1).perform();
		   Thread.sleep(6000);
		   
		   String id_pr = a.readXML("kpi","id_pr");
		   WebElement menuHoverLink2 = driver.findElement(By.id(id_pr));
		   actions.moveToElement(menuHoverLink2).perform();
		   Thread.sleep(6000);
		   
		   String id_1 = a.readXML("prkpi","id_1");
		   WebElement menuHoverLink3 = driver.findElement(By.id(id_1));
		   actions.moveToElement(menuHoverLink3).click().perform();
		   Thread.sleep(6000);

    
		  
    }

	private static void waitforElement(WebDriver driver, int i, String string) {
		// TODO Auto-generated method stub
		
	}

	public String readXML(String searchelement,String tag) throws SAXException, IOException, ParserConfigurationException{
        String ele = null;
        File fXmlFile = new File("D://NewFile.xml");
        DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
        Document doc = dBuilder.parse(fXmlFile);
        doc.getDocumentElement().normalize();
        NodeList nList = doc.getElementsByTagName(searchelement);
        Node nNode = nList.item(0);
        if (nNode.getNodeType() == Node.ELEMENT_NODE) {
        	Element eElement = (Element) nNode;
            ele=eElement.getElementsByTagName(tag).item(0).getTextContent();
        }
        return ele;
    }

}

Fatal Error] NewFile.xml:27:57: The entity name must immediately follow the '&' in the entity reference.
Exception in thread "main" org.xml.sax.SAXParseException; systemId: file:/D:/NewFile.xml; lineNumber: 27; columnNumber: 57; The entity name must immediately follow the '&' in the entity reference.
	at org.apache.xerces.parsers.DOMParser.parse(Unknown Source)
	at org.apache.xerces.jaxp.DocumentBuilderImpl.parse(Unknown Source)
	at javax.xml.parsers.DocumentBuilder.parse(Unknown Source)
	at A.readXML(A.java:94)
	at A.main(A.java:40)