为什么我不能通过从另一个 Class 调用方法来使用 JavaFX 文本字段生成地图？
Why can't I generate a map using JavaFX textfields by calling the method from another Class?
*我是 java/programming 新手。
我编写了以下代码示例来尝试找出我的问题，然后给出我的问题的清晰示例。我想根据它们在应用程序中的功能将我的程序分成单独的 classes：
主要的
MainController - 驱动 JavaFX GUI。
初始化程序 - 输入数据的语义验证。
模型 - 对数据执行计算并将结果发送回 MainController。
我被卡住的地方是初始化程序，特别是 linkedhashmap 和第一次验证检查，抛出一个 nullpointerexception。如果所有内容都在一个 class 中，则不会发生这种情况（我从一个 class 中的所有内容开始，现在正在学习如何在单独的 class 中构建结构，等等）。如果我不使用任何 JavaFX 功能，它也不会发生。
例如，这个有效：
package helloWorld;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello world!");
HashmapExample hashy = new HashmapExample();
System.out.println(hashy.initialiser());
}
}
package helloWorld;
import java.util.LinkedHashMap;
import java.util.Map;
public class HashmapExample {
private Map<String,String> testMap = new LinkedHashMap<>();
public void mapper() {
testMap.put("one","a");
testMap.put("two","b");
testMap.put("three","c");
}
public String initialiser() {
mapper();
String errorField = testMap.entrySet().stream().filter(entry -> entry.getKey().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
String message;
if (errorField != null) {
return message = errorField + " blank!";
} else {
return message = "OK!";
}
}
}
但这不是：
package helloWorldFX;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.VBox;
public class Main extends Application {
@Override
public void start(Stage primaryStage) {
try {
VBox root = (VBox)FXMLLoader.load(getClass().getResource("MainGUI.fxml"));
Scene scene = new Scene(root,400,400);
scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
primaryStage.setScene(scene);
primaryStage.show();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
launch(args);
}
}
package helloWorldFX;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.TextArea;
public class MainController {
@FXML private TextArea outputMessage;
public void run(ActionEvent event) {
Initialiser initialiser = new Initialiser();
outputMessage.setText(initialiser.checker());
}
}
package helloWorldFX;
import java.util.LinkedHashMap;
import java.util.Map;
import javafx.fxml.FXML;
import javafx.scene.control.TextField;
public class Initialiser {
@FXML private TextField one;
@FXML private TextField two;
@FXML private TextField three;
private Map<TextField,String> testMap = new LinkedHashMap<>();
public void mapper() {
testMap.put(one,"a");
testMap.put(two,"b");
testMap.put(three,"c");
}
public String checker() {
mapper();
String errorField = testMap.entrySet().stream().filter(entry -> entry.getKey().getText().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
String message;
if (errorField != null) {
return message = errorField + " blank!";
} else {
return message = "OK!";
}
}
}
当我在 eclipse 中覆盖 运行 时，我可以看出它可能是由行引起的
String errorField = testMap.entrySet().stream().filter(entry -> entry.getKey().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
但我不是很确定。
我刚刚在场景生成器中注意到字段 'one'、'two' 和 'three' 没有显示为文本字段的有效 ID，因为它们不是在 MainController class 中。这一定与问题有关，但我不知道如何解决它。
FXML文件，按要求：请记住，它是一组示例代码，并非真正的程序，因此布局毫无意义。
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.TextArea?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.VBox?>
<VBox prefHeight="300.0" prefWidth="300.0" xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="helloWorldFX.MainController">
<children>
<TextField />
<TextField />
<TextField />
<Button mnemonicParsing="false" onAction="#run" text="Button" />
<TextArea fx:id="outputMessage" prefHeight="200.0" prefWidth="200.0" />
</children>
</VBox>
错误信息：
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1787)
at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1670)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8890)
at javafx.controls/javafx.scene.control.Button.fire(Button.java:203)
at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:206)
at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3862)
at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2590)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:409)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:299)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent(GlassViewEventHandler.java:447)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:411)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:446)
at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:174)
at java.base/java.lang.Thread.run(Thread.java:835)
Caused by: java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:273)
at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1782)
... 46 more
Caused by: java.lang.NullPointerException
at helloWorldFX.Initialiser.lambda[=17=](Initialiser.java:29)
at java.base/java.util.stream.ReferencePipeline.accept(ReferencePipeline.java:176)
at java.base/java.util.Spliterators$IteratorSpliterator.tryAdvance(Spliterators.java:1812)
at java.base/java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:127)
at java.base/java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:502)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:488)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:150)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:543)
at helloWorldFX.Initialiser.checker(Initialiser.java:29)
at helloWorldFX.MainController.run(MainController.java:15)
... 58 more
解决方法：
因此，根据评论和对可能原因的更多思考，我想出了这个解决方法。
我在 MainController 中实例化并填充 Map，然后实例化 Initialiser class，它现在通过构造函数将 Map 作为参数。然后我从 Initialiser 对象调用检查器方法，它对实例化时发送到对象的数据运行语义检查。
据我所知，问题是一个 fxml 文件只能处理一个控制器 class，所以你不能从除主控制器之外的任何地方用 TextFields 填充地图控制器 class。如果这样做，getText 方法将抛出 nullpointerexception，因为它指向的 TextFields 在技术上不存在于 fxml 中。
查看修改后的代码：
package helloWorldFX;
import java.util.LinkedHashMap;
import java.util.Map;
import javafx.fxml.FXML;
import javafx.scene.control.TextField;
import javafx.scene.control.TextArea;
import javafx.event.ActionEvent;
public class MainController {
@FXML private TextField one;
@FXML private TextField two;
@FXML private TextField three;
@FXML private TextArea outputMessage;
public void run(ActionEvent event) {
Map<TextField, String> testMap = new LinkedHashMap<>();
testMap.put(one,"a");
testMap.put(two,"b");
testMap.put(three,"c");
Initialiser initialiser = new Initialiser(testMap);
outputMessage.setText(initialiser.checker());
}
}
package helloWorldFX;
import java.util.Map;
import javafx.scene.control.TextField;
public class Initialiser {
private Map<TextField, String> values;
public Initialiser(Map<TextField, String> mappedValues) {
this.values = mappedValues;
}
String message;
public String checker() {
String errorField = values.entrySet().stream().filter(entry -> entry.getKey().getText().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
if (errorField != null) {
return message = errorField + " blank!";
} else {
return message = "OK!";
}
}
}
在这一点上，由于我缺乏经验，我不知道这是否真的是一种解决方法或真正正确的方法 - 也许有人可以帮助填写这部分内容。
*我是 java/programming 新手。
我编写了以下代码示例来尝试找出我的问题，然后给出我的问题的清晰示例。我想根据它们在应用程序中的功能将我的程序分成单独的 classes： 主要的 MainController - 驱动 JavaFX GUI。 初始化程序 - 输入数据的语义验证。 模型 - 对数据执行计算并将结果发送回 MainController。
我被卡住的地方是初始化程序，特别是 linkedhashmap 和第一次验证检查，抛出一个 nullpointerexception。如果所有内容都在一个 class 中，则不会发生这种情况（我从一个 class 中的所有内容开始，现在正在学习如何在单独的 class 中构建结构，等等）。如果我不使用任何 JavaFX 功能，它也不会发生。
例如，这个有效：
package helloWorld;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello world!");
HashmapExample hashy = new HashmapExample();
System.out.println(hashy.initialiser());
}
}
package helloWorld;
import java.util.LinkedHashMap;
import java.util.Map;
public class HashmapExample {
private Map<String,String> testMap = new LinkedHashMap<>();
public void mapper() {
testMap.put("one","a");
testMap.put("two","b");
testMap.put("three","c");
}
public String initialiser() {
mapper();
String errorField = testMap.entrySet().stream().filter(entry -> entry.getKey().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
String message;
if (errorField != null) {
return message = errorField + " blank!";
} else {
return message = "OK!";
}
}
}
但这不是：
package helloWorldFX;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.VBox;
public class Main extends Application {
@Override
public void start(Stage primaryStage) {
try {
VBox root = (VBox)FXMLLoader.load(getClass().getResource("MainGUI.fxml"));
Scene scene = new Scene(root,400,400);
scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
primaryStage.setScene(scene);
primaryStage.show();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
launch(args);
}
}
package helloWorldFX;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.TextArea;
public class MainController {
@FXML private TextArea outputMessage;
public void run(ActionEvent event) {
Initialiser initialiser = new Initialiser();
outputMessage.setText(initialiser.checker());
}
}
package helloWorldFX;
import java.util.LinkedHashMap;
import java.util.Map;
import javafx.fxml.FXML;
import javafx.scene.control.TextField;
public class Initialiser {
@FXML private TextField one;
@FXML private TextField two;
@FXML private TextField three;
private Map<TextField,String> testMap = new LinkedHashMap<>();
public void mapper() {
testMap.put(one,"a");
testMap.put(two,"b");
testMap.put(three,"c");
}
public String checker() {
mapper();
String errorField = testMap.entrySet().stream().filter(entry -> entry.getKey().getText().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
String message;
if (errorField != null) {
return message = errorField + " blank!";
} else {
return message = "OK!";
}
}
}
当我在 eclipse 中覆盖 运行 时，我可以看出它可能是由行引起的
String errorField = testMap.entrySet().stream().filter(entry -> entry.getKey().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
但我不是很确定。
我刚刚在场景生成器中注意到字段 'one'、'two' 和 'three' 没有显示为文本字段的有效 ID，因为它们不是在 MainController class 中。这一定与问题有关，但我不知道如何解决它。
FXML文件，按要求：请记住，它是一组示例代码，并非真正的程序，因此布局毫无意义。
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.TextArea?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.VBox?>
<VBox prefHeight="300.0" prefWidth="300.0" xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="helloWorldFX.MainController">
<children>
<TextField />
<TextField />
<TextField />
<Button mnemonicParsing="false" onAction="#run" text="Button" />
<TextArea fx:id="outputMessage" prefHeight="200.0" prefWidth="200.0" />
</children>
</VBox>
错误信息：
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1787)
at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1670)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8890)
at javafx.controls/javafx.scene.control.Button.fire(Button.java:203)
at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:206)
at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3862)
at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2590)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:409)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:299)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent(GlassViewEventHandler.java:447)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:411)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:446)
at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop(WinApplication.java:174)
at java.base/java.lang.Thread.run(Thread.java:835)
Caused by: java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:567)
at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:273)
at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1782)
... 46 more
Caused by: java.lang.NullPointerException
at helloWorldFX.Initialiser.lambda[=17=](Initialiser.java:29)
at java.base/java.util.stream.ReferencePipeline.accept(ReferencePipeline.java:176)
at java.base/java.util.Spliterators$IteratorSpliterator.tryAdvance(Spliterators.java:1812)
at java.base/java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:127)
at java.base/java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:502)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:488)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:150)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:543)
at helloWorldFX.Initialiser.checker(Initialiser.java:29)
at helloWorldFX.MainController.run(MainController.java:15)
... 58 more
解决方法：
因此，根据评论和对可能原因的更多思考，我想出了这个解决方法。
我在 MainController 中实例化并填充 Map，然后实例化 Initialiser class，它现在通过构造函数将 Map 作为参数。然后我从 Initialiser 对象调用检查器方法，它对实例化时发送到对象的数据运行语义检查。
据我所知，问题是一个 fxml 文件只能处理一个控制器 class，所以你不能从除主控制器之外的任何地方用 TextFields 填充地图控制器 class。如果这样做，getText 方法将抛出 nullpointerexception，因为它指向的 TextFields 在技术上不存在于 fxml 中。
查看修改后的代码：
package helloWorldFX;
import java.util.LinkedHashMap;
import java.util.Map;
import javafx.fxml.FXML;
import javafx.scene.control.TextField;
import javafx.scene.control.TextArea;
import javafx.event.ActionEvent;
public class MainController {
@FXML private TextField one;
@FXML private TextField two;
@FXML private TextField three;
@FXML private TextArea outputMessage;
public void run(ActionEvent event) {
Map<TextField, String> testMap = new LinkedHashMap<>();
testMap.put(one,"a");
testMap.put(two,"b");
testMap.put(three,"c");
Initialiser initialiser = new Initialiser(testMap);
outputMessage.setText(initialiser.checker());
}
}
package helloWorldFX;
import java.util.Map;
import javafx.scene.control.TextField;
public class Initialiser {
private Map<TextField, String> values;
public Initialiser(Map<TextField, String> mappedValues) {
this.values = mappedValues;
}
String message;
public String checker() {
String errorField = values.entrySet().stream().filter(entry -> entry.getKey().getText().isBlank()).map(Map.Entry::getValue).findFirst().orElse(null);
if (errorField != null) {
return message = errorField + " blank!";
} else {
return message = "OK!";
}
}
}
在这一点上，由于我缺乏经验，我不知道这是否真的是一种解决方法或真正正确的方法 - 也许有人可以帮助填写这部分内容。