Netbeans，empty DefaultListModel

Question

为什么myList是空的？

从输出我可以看到myList没有正确的大小，但消息。

输出：

Apr 23, 2012 4:28:42 PM net.bounceme.dur.nntp.MessagesJFrame <init> 
INFO: messages 11 
Apr 23, 2012 4:28:42 PM net.bounceme.dur.nntp.MessagesJFrame <init> 
INFO: myList 0 

MessagesJFrame：

package net.bounceme.dur.nntp; 

import java.util.List; 
import java.util.logging.Level; 
import java.util.logging.Logger; 
import javax.mail.Message; 
import javax.swing.DefaultListModel; 

public class MessagesJFrame extends javax.swing.JFrame { 

    private static final long serialVersionUID = 1L; 
    private static final Logger LOG = Logger.getLogger(MessagesJFrame.class.getName()); 
    DefaultListModel<Message> myList = new DefaultListModel<Message>(); 

    public MessagesJFrame() { 
     initComponents(); 
     EnumNNTP nntp = EnumNNTP.INSTANCE; 
     List messages = null; 
     try { 
      messages = nntp.getMessages(false); 
     } catch (Exception ex) { 
      LOG.severe("didn't get messages"); 
     } 
     myList.copyInto(messages.toArray()); 
     LOG.log(Level.INFO, "messages {0}", messages.size()); 
     LOG.log(Level.INFO, "myList {0}", myList.size()); 
    } 

    /** 
    * This method is called from within the constructor to initialize the form. 
    * WARNING: Do NOT modify this code. The content of this method is always 
    * regenerated by the Form Editor. 
    */ 
    @SuppressWarnings("unchecked") 
    // <editor-fold defaultstate="collapsed" desc="Generated Code"> 
    private void initComponents() { 

     jScrollPane2 = new javax.swing.JScrollPane(); 
     jList1 = new javax.swing.JList(); 

     setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); 

     jList1.setModel(myList); 
     jScrollPane2.setViewportView(jList1); 

     javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); 
     getContentPane().setLayout(layout); 
     layout.setHorizontalGroup(
      layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup() 
       .addContainerGap(13, Short.MAX_VALUE) 
       .addComponent(jScrollPane2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addGap(129, 129, 129)) 
     ); 
     layout.setVerticalGroup(
      layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addGroup(layout.createSequentialGroup() 
       .addContainerGap() 
       .addComponent(jScrollPane2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addContainerGap(158, Short.MAX_VALUE)) 
     ); 

     pack(); 
    }// </editor-fold> 

    /** 
    * @param args the command line arguments 
    */ 
    public static void main(String args[]) { 
     /* 
     * Set the Nimbus look and feel 
     */ 
     //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) "> 
     /* 
     * If Nimbus (introduced in Java SE 6) is not available, stay with the 
     * default look and feel. For details see 
     * http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */ 

     try { 
      for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) { 
       if ("Nimbus".equals(info.getName())) { 
        javax.swing.UIManager.setLookAndFeel(info.getClassName()); 
        break; 
       } 
      } 
     } catch (ClassNotFoundException ex) { 
      java.util.logging.Logger.getLogger(MessagesJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } catch (InstantiationException ex) { 
      java.util.logging.Logger.getLogger(MessagesJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } catch (IllegalAccessException ex) { 
      java.util.logging.Logger.getLogger(MessagesJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } catch (javax.swing.UnsupportedLookAndFeelException ex) { 
      java.util.logging.Logger.getLogger(MessagesJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); 
     } 
     //</editor-fold> 

     /* 
     * Create and display the form 
     */ 
     java.awt.EventQueue.invokeLater(new Runnable() { 

      public void run() { 
       new MessagesJFrame().setVisible(true); 
      } 
     }); 
    } 
    // Variables declaration - do not modify 
    private javax.swing.JList jList1; 
    private javax.swing.JScrollPane jScrollPane2; 
    // End of variables declaration 
} 

Answer 1

你在哪里的模型添加到JList中？为了使JList能够使用和显示由模型保存的数据，必须通过JList的构造函数或其方法将模型添加到JList中。你有没有通过JList tutorials？如果不是的话，这是你应该看的第一个地方，因为它会解释如何使用JList，然后解释一些。

编辑1
的DefaultListModel copyInto(...)方法做什么，你认为它的对面。它将模型中的数据复制到数组中。

每API：该列表的

复制组件到指定的数组

Answer 2

在最窄意义，下面的代码填充模型：

固定方法：

public MessagesJFrame() { 
    initComponents(); 
    EnumNNTP nntp = EnumNNTP.INSTANCE; 
    List<Message> messages = null; 
    try { 
     messages = nntp.getMessages(false); 
    } catch (Exception ex) { 
     LOG.severe("didn't get messages"); 
    } 
    for (Message m : messages) { 
     myList.addElement(m); 
    } 
    LOG.log(Level.INFO, "messages {0}", messages.size()); 
    LOG.log(Level.INFO, "myList {0}", myList.size()); 
} 

但是，有什么问题？

上面的代码输出消息和myList的大小相同。