java - JavaFX (java.lang.NullPointerException)
问题描述
这是在我有 setItems(oblist) 的 TableController 文件中启动 FXML 的文件，这是错误的来源。它说我的代码中的某些内容指向 NULL。我正在尝试使用 mySQL 数据库中的数据插入 GUI，但无法启动 GUI。这是我一直关注的 youtube 视频的链接。https://www.youtube.com/watch?v=LoiQVoNil9Q
package cheapflights.system.gui;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class JavaFXDB extends Application{
@Override
public void start(Stage stage) throws Exception {
// TODO Auto-generated method stub
Parent root = FXMLLoader.load(getClass().getResource("GUIGUI.fxml"));
Scene scene = new Scene(root);
stage.setScene(scene);
stage.show();
}
public static void main(String[] args) {
launch(args);
}
}
这是主要代码/控制器
package cheapflights.system.gui;
import javafx.fxml.FXML;
import javafx.scene.control.Label;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import java.net.URL;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ResourceBundle;
import java.util.logging.Level;
import java.util.logging.Logger;
import com.mysql.cj.conf.IntegerProperty;
import javafx.fxml.Initializable;
import javafx.beans.property.StringProperty;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.fxml.FXML;
import javafx.scene.*;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.control.cell.PropertyValueFactory;
public class TableController implements Initializable {
@FXML
private TableView<ModelTable> table;
@FXML
private TableColumn<ModelTable,IntegerProperty> col_flightID;
@FXML
private TableColumn<ModelTable,StringProperty> col_departingCity;
@FXML
private TableColumn<ModelTable,StringProperty> col_arrivalCity;
@FXML
private TableColumn<ModelTable,StringProperty> col_departureTime;
@FXML
private TableColumn<ModelTable,StringProperty> col_arrivalTime;
@FXML
private TableColumn<ModelTable,StringProperty> col_flightDate;
@FXML
private TableColumn<ModelTable,IntegerProperty> col_Quantity;
ObservableList<ModelTable> oblist = FXCollections.observableArrayList();
@Override
public void initialize(URL location, ResourceBundle resources) {
// TODO Auto-generated method stub
Connection myConn = null;
Statement myStmt = null;
ResultSet myRs = null;
try {
myConn = DriverManager.getConnection("jdbc:mysql://localhost:3306/demo", "flightuser" , "flightuser");
myStmt = myConn.createStatement();
// 3. Execute SQL query
myRs = myStmt.executeQuery("select * from Flight");
while (myRs.next()) {
oblist.add(new ModelTable(myRs.getInt("flightID"), myRs.getString("departingCity"),
myRs.getString("arrivalCity"), myRs.getString("departureTime"), myRs.getString("arrivalTime"), myRs.getString("flightDate"), myRs.getInt("Quantity") ));
}
} catch (SQLException ex) {
// TODO Auto-generated catch block
Logger.getLogger(TableController.class.getName()).log(Level.SEVERE, null, ex);
}
col_flightID.setCellValueFactory(new PropertyValueFactory<>("flightID"));
col_departingCity.setCellValueFactory(new PropertyValueFactory<>("departingCity"));
col_arrivalCity.setCellValueFactory(new PropertyValueFactory<>("arrivalCity"));
col_departureTime.setCellValueFactory(new PropertyValueFactory<>("departureTime"));
col_arrivalTime.setCellValueFactory(new PropertyValueFactory<>("arrivalTime"));
col_flightDate.setCellValueFactory(new PropertyValueFactory<>("flightDate"));
col_Quantity.setCellValueFactory(new PropertyValueFactory<>("Quantity"));
table.setItems(oblist);
}
}
这是模型表
package cheapflights.system.gui;
public class ModelTable {
private int flightID;
private String departingCity;
private String arrivalCity;
private String departureTime;
private String arrivalTime;
private String flightDate;
private int Quantity;
public ModelTable(int flightID, String departingCity, String arrivalCity,String departureTime, String arrivalTime, String flightDate, int Quantity) {
this.flightID = flightID;
this.departingCity = departingCity;
this.arrivalCity= arrivalCity;
this.departureTime = departureTime;
this.arrivalTime = arrivalTime;
this.flightDate = flightDate;
this.Quantity = Quantity;
}
public int getFlight() {
return flightID;
}
public void setFlight(int flightID) {
this.flightID = flightID;
}
public String getarrivalTime() {
return arrivalTime;
}
public void setarrivalTime(String arrivalTime) {
this.arrivalTime = arrivalTime;
}
public String getdepartureTime() {
return departureTime;
}
public void setdepatureTime(String departureTime) {
this.departureTime = departureTime;
}
public String getdepartingCity() {
return departingCity;
}
public void setdepartingCity(String departingCity) {
this.departingCity = departingCity;
}
public String getarrivalCity() {
return arrivalCity;
}
public void setarrivalCity(String arrivalCity) {
this.arrivalCity = arrivalCity;
}
public String getflightDate() {
return flightDate;
}
public void setflightDate(String flightDate) {
this.flightDate = flightDate;
}
public int getQuantity() {
return Quantity;
}
public void setquntity(int Quantity) {
this.Quantity = Quantity;
}
}
这是 FXML 文件
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.layout.AnchorPane?>
<AnchorPane xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/8" fx:controller = "cheapflights.system.gui.TableController">
<children>
<TableView layoutX="-222.0" layoutY="-32.0" prefHeight="410.0" prefWidth="562.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
<columns>
<TableColumn fx:id="col_flightID" prefWidth="71.0" text="flightID" />
<TableColumn fx:id="col_departingCity" prefWidth="71.0" text="departingCity" />
<TableColumn fx:id="col_arrivalCity" prefWidth="89.0" text="arrivalCity" />
<TableColumn fx:id="col_departureTime" prefWidth="75.0" text="departureTime" />
<TableColumn fx:id="col_arrivalTime" prefWidth="95.0" text="arrivalTime" />
<TableColumn fx:id="col_flightDate" minWidth="0.0" prefWidth="82.0" text="flightDate" />
<TableColumn fx:id="col_Quantity" minWidth="0.0" prefWidth="73.0" text="Quantity" />
</columns>
</TableView>
</children>
</AnchorPane>
这是运行时错误
Exception in Application start method
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$154(LauncherImpl.java:182)
at java.lang.Thread.run(Thread.java:748)
Caused by: javafx.fxml.LoadException:
/home/dvd86/git/cis3270-project/TermProject/bin/cheapflights/system/gui/GUIGUI.fxml
at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2601)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2579)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3214)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3175)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3148)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3124)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3104)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3097)
at cheapflights.system.gui.JavaFXDB.start(JavaFXDB.java:14)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$161(LauncherImpl.java:863)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$174(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl.lambda$null$172(PlatformImpl.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$173(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
at com.sun.glass.ui.gtk.GtkApplication.lambda$null$48(GtkApplication.java:139)
... 1 more
Caused by: java.lang.NullPointerException
at cheapflights.system.gui.TableController.initialize(TableController.java:87)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
... 17 more
Exception running application cheapflights.system.gui.JavaFXDB
这是运行时错误中显示的特定错误
Caused by: java.lang.NullPointerException
at cheapflights.system.gui.TableController.initialize(TableController.java:87)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
... 17 more
Exception running application cheapflights.system.gui.JavaFXDB
解决方案
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