我正忙着学习JavaFX的小项目。 当我做一个特定的动作时，我得到一个NullPointer，我无法弄清楚为什么会出现这个错误。
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at org.hva.klm.projectagiledevelopment.MedewerkerMainController.databaseVrachtShow(MedewerkerMainController.java:308)
at org.hva.klm.projectagiledevelopment.MedewerkerMainController$1.handle(MedewerkerMainController.java:272)
at org.hva.klm.projectagiledevelopment.MedewerkerMainController$1.handle(MedewerkerMainController.java:260)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8411)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$355(GlassViewEventHandler.java:388)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$149(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
这些是发生错误的Controller类中的方法：
@FXML
public void zoekVracht() {
actionError.setText(" ");
try {
// Check if field is empty
if (ZoekVrachtInvoer.getText().equals("")) {
actionError.setFill(Color.FIREBRICK);
actionError.setText("Geen invoer... Probeer nogmaals.");
} else {
//database connection for first user
Statement statement = dbCon.conDatabase().createStatement();
//getting count for buttonList size
ResultSet resultCount = statement.executeQuery("SELECT COUNT(*)"
+ " from reservatie"
+ " where idReservatie like '%" + ZoekVrachtInvoer.getText() + "%'");
resultCount.next();
numberOfRows = resultCount.getInt(1);
// Select all reservations which meet the textfield characters
ResultSet rs = statement.executeQuery("SELECT * from reservatie "
+ "where idReservatie like '%"
+ ZoekVrachtInvoer.getText() + "%';"
);
// Check if any reservations exsists
if (!rs.next()) {
actionError.setFill(Color.FIREBRICK);
actionError.setText("Barcode niet gevonden");
// List all found barcodes
} else {
i = 0;
rs.beforeFirst();
buttonList = new Button[numberOfRows];
while (rs.next()) {
final int account_id = rs.getInt("idReservatie");
String username = rs.getString("Naam");
String firstname = rs.getString("gewicht");
String lastname = rs.getString("Lengte");
// int status = rs.getInt("status");
gpTable.add(new Label(username), 0, i);
gpTable.add(new Label(firstname), 1, i);
gpTable.add(new Label(lastname), 2, i);
buttonList[i] = new Button("Edit reservatie");
gpTable.add(buttonList[i], 4, i);
buttonList[i].setOnAction(new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent event) {
try {
Parent home_page_parent = FXMLLoader.load(FXMLDocumentController.class.getResource("FXMLInvoerVracht2.fxml"));
Scene home_page_scene = new Scene(home_page_parent);
Stage app_stage = (Stage) ((Node) event.getSource()).getScene().getWindow();
app_stage.hide();
app_stage.setScene(home_page_scene);
app_stage.show();
databaseVrachtShow(account_id);
System.out.println(account_id);
} catch (IOException ex) {
Logger.getLogger(MedewerkerMainController.class.getName()).log(Level.SEVERE, null, ex);
}
}
});
i++;
}
}
}
} catch (SQLException ex) {
Logger.getLogger(MedewerkerMainController.class.getName())
.log(Level.SEVERE, null, ex);
} finally {
try {
dbCon.conDatabase().close();
} catch (Exception ex) {
Logger.getLogger(MedewerkerMainController.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
和
@FXML
public void databaseVrachtShow(int account_id) {
System.out.println(account_id);
try {
Statement statement = dbCon.conDatabase().createStatement();
ResultSet resultSet = statement.executeQuery("SELECT * from reservatie "
+ "where idReservatie = " + account_id + "");
while (resultSet.next()) {
// NaamDatabase.setText(resultSet.getString("Naam"));
GewichtDatabase.setText(resultSet.getString("Gewicht"));
LengteDatabase.setText(resultSet.getString("Lengte"));
BreedteDatabase.setText(resultSet.getString("Breedte"));
HoogteDatabase.setText(resultSet.getString("Hoogte"));
//DatumDatabase.setText(resultSet.getString("Nog open"));
}
} catch (SQLException ex) {
Logger.getLogger(MedewerkerMainController.class.getName()).log(Level.SEVERE, null, ex);
} finally {
try {
dbCon.conDatabase().close();
} catch (Exception ex) {
Logger.getLogger(MedewerkerMainController.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
此行发生错误：GewichtDatabase.setText（resultSet.getString（“Gewicht”））; 不知何故，标签不能设置为getString应该获取的值。 所有标签都有自己的ID等。
根据要求：“
@FXML
private Label GewichtDatabase;
@FXML
private Label LengteDatabase;
@FXML
private Label BreedteDatabase;
@FXML
private Label HoogteDatabase;
和fxml文件代码：
<Label fx:id="GewichtDatabase" layoutX="526.0" layoutY="106.0" />
<Label fx:id="LengteDatabase" layoutX="526.0" layoutY="134.0" />
<Label fx:id="BreedteDatabase" layoutX="526.0" layoutY="164.0" />
<Label fx:id="HoogteDatabase" layoutX="526.0" layoutY="195.0" />
有人能帮助我吗？