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我正在編寫代碼以從MySQL數據庫檢索數據。
我想將查詢的一列添加到JList。異常將元素添加到JList
這是我的代碼：
try {
ArrayList<String> names = new ArrayList();
db = new Database();
db.connect();
Statement st = db.getConnection().createStatement();
ResultSet rs = st.executeQuery("SELECT nombre FROM alumnos");
while (rs.next()) {
names.add(rs.getString("nombre"));
}
DefaultListModel listModel = new DefaultListModel();
for(String nms : names) {
listModel.addElement(nms);
}
//This is the line 140
// and lstInicio is the JList
lstInicio.setModel(listModel);
} catch (SQLException sql) {
System.err.println(sql.getMessage());
}
我覺得一切都很好，但是當我到達這部分代碼我得到一個異常：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at proyecto.ausentismo.MainWindow.loadList(MainWindow.java:140)
at proyecto.ausentismo.MainWindow.<init>(MainWindow.java:21)
at proyecto.ausentismo.Login.btnLoginActionPerformed(Login.java:121)
at proyecto.ausentismo.Login.access$000(Login.java:11)
at proyecto.ausentismo.Login$1.actionPerformed(Login.java:49)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener$Actions.actionPerformed(BasicButtonListener.java:303)
at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1664)
at javax.swing.JComponent.processKeyBinding(JComponent.java:2879)
at javax.swing.JComponent.processKeyBindings(JComponent.java:2926)
at javax.swing.JComponent.processKeyEvent(JComponent.java:2842)
at java.awt.Component.processEvent(Component.java:6282)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1895)
at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:762)
at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:1027)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:899)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:727)
at java.awt.Component.dispatchEventImpl(Component.java:4731)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
有誰知道是什麼原因造成這例外？我怎麼知道？ 編輯：我評論了錯誤的行。並stil得到異常
你可以給你的代碼塊添加一個註釋，指出哪一行是MainWindow行140（錯誤跟蹤說的是異常的來源）？ – Bobulous 2013-05-02 22:32:22
我第二@Arkanon請求。如果錯誤出現在上面的代碼中，我的賭注就在這一行：'lstInicio.setModel（listModel）;'和'lstInicio'爲null。如果是這樣，那麼在使用它之前你沒有正確初始化這個變量。 – 2013-05-02 22:41:09
他必須缺少在他的代碼中創建對象'DefaultListModel listModel = new DefaultListModel（）;' – 2013-05-02 23:22:51