我有这个类，它应该向 JPanel 添加一个 JLabel，但由于某种原因它没有这样做。为什么不将 JLabel 添加到 JPanel？这发生在我的SwigWorker课堂上的done()方法中
package sscce;
import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.ArrayList;
import javax.swing.JLabel;
import javax.swing.SwingWorker;
import javax.swing.UIManager;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.CharacterData;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
public class sscce extends javax.swing.JFrame{
protected XML xml = new XML();
public sscce(){
initComponents();
GetNotes getNotes = new GetNotes();
getNotes.execute();
}
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
jScrollPane1 = new javax.swing.JScrollPane();
notesPanel = new javax.swing.JPanel();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
javax.swing.GroupLayout notesPanelLayout = new javax.swing.GroupLayout(notesPanel);
notesPanel.setLayout(notesPanelLayout);
notesPanelLayout.setHorizontalGroup(
notesPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGap(0, 494, Short.MAX_VALUE)
);
notesPanelLayout.setVerticalGroup(
notesPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGap(0, 433, Short.MAX_VALUE)
);
jScrollPane1.setViewportView(notesPanel);
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 496, Short.MAX_VALUE)
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 435, Short.MAX_VALUE)
);
pack();
}// </editor-fold>
public static void main(String args[]){
try{
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
}catch( ClassNotFoundException | InstantiationException | IllegalAccessException | javax.swing.UnsupportedLookAndFeelException ex){
java.util.logging.Logger.getLogger(sscce.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
java.awt.EventQueue.invokeLater(new Runnable(){
public void run(){
new sscce().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JPanel notesPanel;
// End of variables declaration
public class GetNotes extends SwingWorker{
protected ArrayList<XML> notes;
@Override
public void done(){
System.out.println(notes.size());
for(XML note : notes){
String n = note.getNode("notes", "note");
System.out.println(n);
JLabel lbl = new JLabel(n);
lbl.setVisible(true);
notesPanel.add(lbl);
}
}
@Override
public String doInBackground(){
String xmlStr = "<?xml version=\"1.0\"?>"
+ "<root>"
+ " <success>true</success>"
+ " <notes>"
+ " <note>Note 1</note>"
+ " </notes>"
+ " <notes>"
+ " <note>Note 2</note>"
+ " </notes>"
+ " <notes>"
+ " <note>Note 3</note>"
+ " </notes>"
+ "</root>";
xml.parse(xmlStr);
notes = xml.getNodes("root", "notes");
return null;
}
}
}
class XML{
private Document doc;
public XML(){
}
public void parse(String xml){
try{
DocumentBuilder db = DocumentBuilderFactory.newInstance().newDocumentBuilder();
InputSource is = new InputSource();
is.setCharacterStream(new StringReader(xml));
doc = db.parse(is);
}catch(ParserConfigurationException | SAXException | IOException ex){
//Logger.getLogger(XML.class.getName()).log(Level.SEVERE, null, ex);
}
}
public Document getDoc(){
return this.doc;
}
public ArrayList<XML> getNodes(String root, String name){
ArrayList<XML> elList = new ArrayList<>();
NodeList nodes = doc.getElementsByTagName(root);
for(int i = 0; i < nodes.getLength(); i++){
Element element = (Element)nodes.item(i);
NodeList nl = element.getElementsByTagName(name);
for(int c = 0; c < nl.getLength(); c++){
Element e = (Element)nl.item(c);
String xmlStr = this.nodeToString(e);
XML xml = new XML();
xml.parse(xmlStr);
elList.add(xml);
}
}
return elList;
}
private String nodeToString(Node node){
StringWriter sw = new StringWriter();
try{
Transformer t = TransformerFactory.newInstance().newTransformer();
t.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
t.transform(new DOMSource(node), new StreamResult(sw));
}catch(TransformerException te){
System.out.println("nodeToString Transformer Exception");
}
return sw.toString();
}
public String getNode(String root, String name){
NodeList nodes = doc.getElementsByTagName(root);
for(int i = 0; i < nodes.getLength(); i++){
Element element = (Element)nodes.item(i);
NodeList n = element.getElementsByTagName(name);
Element e = (Element)n.item(0);
return getCharacterDataFromElement(e);
}
return "";
}
public static String getCharacterDataFromElement(Element e){
Node child = e.getFirstChild();
if(child instanceof CharacterData){
CharacterData cd = (CharacterData)child;
return cd.getData();
}
return "";
}
}