Java 使用choiceBox和数组时出现NullpointerException错误
我试图让两个不同的选择框同时工作，但是在initialize方法中出现了null指针错误。这有点奇怪，因为我试图初始化选择框中的内容，但是IDE给了我一个空指针异常 这是我的密码Java 使用choiceBox和数组时出现NullpointerException错误,java,javafx,Java,Javafx,我试图让两个不同的选择框同时工作，但是在initialize方法中出现了null指针错误。这有点奇怪，因为我试图初始化选择框中的内容，但是IDE给了我一个空指针异常 这是我的密码 package application; import java.net.URL; import java.util.ArrayList; import java.util.Iterator; import java.util.ResourceBundle; import javafx.event.ActionEve
package application;
import java.net.URL;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ResourceBundle;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ChoiceBox;
import javafx.scene.control.Label;
import javafx.scene.control.ListView;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.scene.Parent;
import javafx.stage.Stage;
public class SampleController implements Initializable{
public static piece PieceClicked = new piece();
ArrayList <Integer> possibleMoves = new ArrayList <Integer>();
ListView<Integer> listView = new ListView<Integer>();
private int enemyLocation;
private boolean valid = true;
@FXML
ChoiceBox<String> inputPieceType, inputPieceAllience;
String[] pieces = {"CANNON","CHARIOT","ELAPHANT","GENERAL","GUARD","HORSES","SOLDIERS"};
String[] allience = {"GREEN","RED"};
@Override
public void initialize(URL arg0, ResourceBundle arg1) {
inputPieceType.getItems().addAll(pieces);
inputPieceAllience.getItems().addAll(allience);
inputPieceType.setOnAction(this::setPiece);
inputPieceAllience.setOnAction(this::setAllience);
}
public void setPiece(ActionEvent event) {
PieceClicked.setPieceType(inputPieceType.getValue());
}
public void setAllience(ActionEvent event) {
PieceClicked.setPieceAllience(inputPieceAllience.getValue());
}
}
Exception in Application start method
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:564)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:464)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363)
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:564)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051)
Caused by: java.lang.RuntimeException: Exception in Application start method
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:900)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication$2(LauncherImpl.java:195)
at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: javafx.fxml.LoadException:
/Users/owenpark/eclipse/java-2020-06/Eclipse.app/Contents/MacOS/computerIA/computerScienceIA/bin/application/Sample.fxml
at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2677)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3323)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3280)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3249)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3222)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3199)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3192)
at application.Main.start(Main.java:13)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(LauncherImpl.java:846)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$12(PlatformImpl.java:455)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:428)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:427)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
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:564)
at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
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.loadImpl(FXMLLoader.java:2673)
... 14 more
Caused by: java.lang.NullPointerException
at application.SampleController.initialize(SampleController.java:62)
... 25 more
Exception running application application.Main
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.ChoiceBox?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.ListView?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.image.Image?>
<?import javafx.scene.image.ImageView?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.text.Text?>
<AnchorPane prefHeight="403.0" prefWidth="839.0" xmlns="http://javafx.com/javafx/15.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.SampleController">
<children>
<AnchorPane layoutX="1.0" layoutY="2.0" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="837.0">
<children>
<ImageView fitHeight="310.0" fitWidth="312.0" layoutX="14.0" layoutY="45.0">
<image>
<Image url="@../../../../../../../../../Documents/computer%20science%20IA%20photos/thumb-data_illust_Jang_Gi_Pan_1440x1440.jpeg" />
</image>
</ImageView>
<VBox layoutX="443.0" layoutY="43.0" prefHeight="315.0" prefWidth="146.0">
<children>
<Text strokeType="OUTSIDE" strokeWidth="0.0" text="location: " />
<TextField fx:id="input" />
<Text strokeType="OUTSIDE" strokeWidth="0.0" text="piece: " />
<ChoiceBox fx:id="inputPieceType" prefWidth="150.0" />
<Text strokeType="OUTSIDE" strokeWidth="0.0" text="Allience: " />
<ChoiceBox fx:id="inputPieceAllience" prefWidth="150.0" />
<Text strokeType="OUTSIDE" strokeWidth="0.0" text="enemy piece location: " />
<TextField fx:id="inputEnemyPieceLocation" prefHeight="32.0" prefWidth="146.0" />
</children>
</VBox>
<Button layoutX="332.0" layoutY="52.0" mnemonicParsing="false" prefHeight="27.0" prefWidth="33.0">
<graphic>
<ImageView fitHeight="22.0" fitWidth="27.0" pickOnBounds="true" preserveRatio="true">
<image>
<Image url="@../../../../../../../../../Documents/computer%20science%20IA%20photos/Green_King.png" />
</image>
</ImageView>
</graphic>
</Button>
<Button layoutX="332.0" layoutY="91.0" mnemonicParsing="false" prefHeight="27.0" prefWidth="33.0">
<graphic>
<ImageView fitHeight="22.0" fitWidth="26.0" pickOnBounds="true" preserveRatio="true">
<image>
<Image url="@../../../../../../../../../Documents/computer%20science%20IA%20photos/Green_Cha.png" />
</image>
</ImageView>
</graphic>
</Button>
<Button layoutX="332.0" layoutY="133.0" mnemonicParsing="false" prefHeight="27.0" prefWidth="33.0">
<graphic>
<ImageView fitHeight="21.0" fitWidth="25.0" pickOnBounds="true" preserveRatio="true">
<image>
<Image url="@../../../../../../../../../Documents/computer%20science%20IA%20photos/Green_Cannon.png" />
</image>
</ImageView>
</graphic>
</Button>
<Button layoutX="332.0" layoutY="171.0" mnemonicParsing="false" prefHeight="32.0" prefWidth="42.0">
<graphic>
<ImageView fitHeight="23.0" fitWidth="24.0" pickOnBounds="true" preserveRatio="true">
<image>
<Image url="@../../../../../../../../../Documents/computer%20science%20IA%20photos/green_Elephant.jpeg" />
</image>
</ImageView>
</graphic>
</Button>
<Button layoutX="332.0" layoutY="214.0" mnemonicParsing="false" prefHeight="31.0" prefWidth="42.0">
<graphic>
<ImageView fitHeight="20.0" fitWidth="37.0" pickOnBounds="true" preserveRatio="true">
<image>
<Image url="@../../../../../../../../../Documents/computer%20science%20IA%20photos/Green_Horse.png" />
</image>
</ImageView>
</graphic>
</Button>
<Button layoutX="332.0" layoutY="255.0" mnemonicParsing="false" prefHeight="33.0" prefWidth="42.0">
<graphic>
<ImageView fitHeight="20.0" fitWidth="67.0" pickOnBounds="true" preserveRatio="true">
<image>
<Image url="@../../../../../../../../../Documents/computer%20science%20IA%20photos/Green_Soldier.png" />
</image>
</ImageView>
</graphic>
</Button>
<Button layoutX="332.0" layoutY="296.0" mnemonicParsing="false" prefHeight="33.0" prefWidth="42.0">
<graphic>
<ImageView fitHeight="20.0" fitWidth="33.0" pickOnBounds="true" preserveRatio="true">
<image>
<Image url="@../../../../../../../../../Documents/computer%20science%20IA%20photos/Green_Guard.png" />
</image>
</ImageView>
</graphic>
</Button>
<Text layoutX="39.0" layoutY="56.0" strokeType="OUTSIDE" strokeWidth="0.0" text="1 2 3 4 5 6 7 8 9" wrappingWidth="270.7308011274751" />
<Text layoutX="29.0" layoutY="72.0" strokeType="OUTSIDE" strokeWidth="0.0" text="1" wrappingWidth="8.67726926690625" />
<Text layoutX="29.0" layoutY="98.0" strokeType="OUTSIDE" strokeWidth="0.0" text="2" wrappingWidth="8.67726926690625" />
<Text layoutX="29.0" layoutY="129.0" strokeType="OUTSIDE" strokeWidth="0.0" text="3" wrappingWidth="8.67726926690625" />
<Text layoutX="27.0" layoutY="157.0" strokeType="OUTSIDE" strokeWidth="0.0" text="4" wrappingWidth="8.67726926690625" />
<Text layoutX="27.0" layoutY="189.0" strokeType="OUTSIDE" strokeWidth="0.0" text="5" wrappingWidth="8.67726926690625" />
<Text layoutX="29.0" layoutY="218.0" strokeType="OUTSIDE" strokeWidth="0.0" text="6" wrappingWidth="8.67726926690625" />
<Text layoutX="29.0" layoutY="248.0" strokeType="OUTSIDE" strokeWidth="0.0" text="7" wrappingWidth="8.67726926690625" />
<Text layoutX="29.0" layoutY="279.0" strokeType="OUTSIDE" strokeWidth="0.0" text="8" wrappingWidth="8.67726926690625" />
<Text layoutX="29.0" layoutY="309.0" strokeType="OUTSIDE" strokeWidth="0.0" text="9" wrappingWidth="8.67726926690625" />
<Text layoutX="22.0" layoutY="335.0" strokeType="OUTSIDE" strokeWidth="0.0" text="10" wrappingWidth="20.65190019321369" />
<Button fx:id="enterButton" layoutX="452.0" layoutY="359.0" mnemonicParsing="false" onAction="#enterButton" text="Input" />
<Button fx:id="clear" layoutX="516.0" layoutY="359.0" mnemonicParsing="false" onAction="#clear" text="clear" />
<Text layoutX="380.0" layoutY="72.0" strokeType="OUTSIDE" strokeWidth="0.0" text="GENERAL" />
<Text layoutX="381.0" layoutY="110.0" strokeType="OUTSIDE" strokeWidth="0.0" text="CHARIOT" />
<Text layoutX="382.0" layoutY="153.0" strokeType="OUTSIDE" strokeWidth="0.0" text="CANNON" />
<Text layoutX="379.0" layoutY="189.0" strokeType="OUTSIDE" strokeWidth="0.0" text="ELEPHANT" />
<Text layoutX="382.0" layoutY="234.0" strokeType="OUTSIDE" strokeWidth="0.0" text="HORSE" />
<Text layoutX="382.0" layoutY="276.0" strokeType="OUTSIDE" strokeWidth="0.0" text="SOLDIER" />
<Text layoutX="386.0" layoutY="317.0" strokeType="OUTSIDE" strokeWidth="0.0" text="GUARD" />
<VBox layoutX="589.0" layoutY="42.0" prefHeight="317.0" prefWidth="126.0">
<children>
<Text strokeType="OUTSIDE" strokeWidth="0.0" text="location:" />
<Label fx:id="locationCheck" prefHeight="25.0" prefWidth="126.0" />
<Text strokeType="OUTSIDE" strokeWidth="0.0" text="piece Type: " />
<Label fx:id="pieceCheck" prefHeight="36.0" prefWidth="126.0" />
<Text strokeType="OUTSIDE" strokeWidth="0.0" text="Allience: " />
<Label fx:id="allianceCheck" prefHeight="31.0" prefWidth="128.0" />
<Text strokeType="OUTSIDE" strokeWidth="0.0" text="enemy piece location:" />
<Label fx:id="enemyLocationCheck" prefHeight="33.0" prefWidth="127.0" />
<Text strokeType="OUTSIDE" strokeWidth="0.0" text="error message:" wrappingWidth="123.269287109375" />
<Label fx:id="errorMessage" prefHeight="35.0" prefWidth="129.0" />
</children>
</VBox>
<Text layoutX="607.0" layoutY="28.0" strokeType="OUTSIDE" strokeWidth="0.0" text="validity check" />
<Text layoutX="723.0" layoutY="27.0" strokeType="OUTSIDE" strokeWidth="0.0" text="Possible Possition" />
<Text layoutX="710.0" layoutY="301.0" strokeType="OUTSIDE" strokeWidth="0.0" text="can this piece be taken" />
<Label fx:id="PieceTake" layoutX="708.0" layoutY="305.0" prefHeight="23.0" prefWidth="126.0" />
</children>
</AnchorPane>
<ListView fx:id="listView" layoutX="715.0" layoutY="40.0" prefHeight="248.0" prefWidth="113.0" />
<Button fx:id="exitButton" layoutX="779.0" layoutY="361.0" mnemonicParsing="false" onAction="#exitButton" prefHeight="27.0" prefWidth="47.0" text="exit" />
</children>
</AnchorPane>
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.text.Font?>
<?import javafx.scene.text.Text?>
<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/15.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.SampleController">
<children>
<Text layoutX="143.0" layoutY="53.0" strokeType="OUTSIDE" strokeWidth="0.0" text="welcome to janggi!">
<font>
<Font size="40.0" />
</font>
</Text>
<Button fx:id="gameButton" layoutX="205.0" layoutY="85.0" mnemonicParsing="false" onAction="#gameButton" prefHeight="74.0" prefWidth="190.0" text="Game Play">
<font>
<Font size="22.0" />
</font>
</Button>
<Button fx:id="explanationButton" layoutX="205.0" layoutY="225.0" mnemonicParsing="false" onAction="#explanationButton" prefHeight="74.0" prefWidth="190.0" text="Explanation">
<font>
<Font size="22.0" />
</font>
</Button>
</children>
</AnchorPane>
问题在于，您从未说过
新选项框inputPieceType.getItems（）.addAll（pieces）引用它们时或inputPieceAllience.getItems（）.addAll（allience）在第62行，他们正在调用从未创建过的项的方法
您可以执行以下操作来初始化对象：
。。。
私人互联网地址；
private boolean valid=true；
@FXML
ChoiceBox inputPieceType=新的ChoiceBox（）；
@FXML
ChoiceBox inputPieceAllience=新的ChoiceBox（）；
弦[]件={“大炮”、“战车”、“埃拉芬特”、“将军”、“卫兵”、“马”、“士兵”}；
字符串[]allience={“绿色”，“红色”}；
...
确保在main方法中加载的.fxml文件位于正确的路径（类路径）
如果您进行了验证，请确保您在控制器中声明的变量名带有@FXML注释
@FXML
选择框inputPieceType、inputPieceAllience；
比较.fxml文件是否存在相同的键入错误。若不匹配，javafx将无法在控制器中自动连接ChoiceBox类，并导致空指针异常
只是一个建议，每当您使用场景生成器进行更改（UI组件）时，请刷新您的.fxml文件，因为eclipse有时需要时间来刷新它
编辑：
实际问题是，SampleController
链接到两个不同的.fxml
文件，并且只加载了Sample.fxml
文件，该文件不包含ChoiceBox
es。这可以通过使用两个单独的控制器来解决，每个.fxml
文件对应一个控制器，然后同时加载这两个控制器
旧答案：
在JavaFX控制器中，标记有@FXML
标记的字段的值由JavaFX运行时从与控制器关联的.FXML
文件中定义的控件注入
在您的例子中，控制器中有两个ChoiceBox
实例，因此您还需要在.fxml
-文件中定义两个ChoiceBox
实例。要让运行时知道哪个控件要链接到控制器中的哪个字段，您需要在.fxml
文件中的每个控件上添加一个fx:id=“fieldName”
。不要忘记将值从fieldName
更改为控制器中字段的相应名称，在您的情况下，其中一个字段的值为inputPieceType
，另一个字段的值为inputPieceAllience
.fxml
文件将如下所示：
<ChoiceBox fx:id="inputPieceType" [other properties...] />
如果不确定控制器类是否连接到.fxml
文件，可以通过查找.fxml
文件中的fx:controller=“com.example.MyController”
属性来查看。com.example.MyController
将是控制器类的全名，在您的例子中应该是application.SampleController
请注意，您还可以在cod中设置控制器
<ChoiceBox fx:id="inputPieceType" [other properties...] />