我正在用Java（抵押贷款计算器）编写一个程序，带有一个GUI，在大学课堂上使用SceneBuilder/FXML，我遇到了一些错误

我还是Java的初学者，很难理解像这个程序这样的东西。然而，我想我终于掌握了它。不幸的是，每当我尝试运行我的程序时，都会出现错误，我不确定如何修复它们

编辑：我还应该声明我需要滑块在值10、20和30之间移动

这是我的控制器程序：

// Controller that handles calculateButton and loanDurationSlider events
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.text.NumberFormat;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.Label;
import javafx.scene.control.Slider;
import javafx.scene.control.TextField;

public class MortgageCalculatorController { 
   // formatters for currency and percentages
   private static final NumberFormat currency = 
      NumberFormat.getCurrencyInstance();
   private static final NumberFormat percent = 
              NumberFormat.getPercentInstance();
   
   // GUI controls defined in FXML and used by the controller's code
   @FXML 
   private TextField purchasePriceTextField; 

   @FXML
   private Label loanDurationLabel; 

   @FXML
   private Slider loanDurationSlider;

   @FXML
   private TextField loanDurationTextField;
   
   @FXML
   private TextField downPaymentTextField;
   
   @FXML
   private TextField interestRateTextField;

   @FXML
   private TextField monthlyPaymentTextField;
   
   private int loanDuration = Integer.parseInt(loanDurationTextField.getText());

   @FXML
   private void calculateButtonPressed(ActionEvent event) {
      try {
         BigDecimal purchasePrice = new BigDecimal(purchasePriceTextField.getText());
         BigDecimal downPayment = new BigDecimal(downPaymentTextField.getText());
         BigDecimal interestRate = new BigDecimal(interestRateTextField.getText());
         BigDecimal twelve = new BigDecimal(12.0);
         BigDecimal hundred = new BigDecimal(100.0);
         interestRate = interestRate.divide(twelve);
         BigDecimal numerator = interestRate.multiply(interestRate.add(BigDecimal.ONE).pow(loanDuration*12));
         BigDecimal denominator = interestRate.add(BigDecimal.ONE).pow(loanDuration*12).subtract(BigDecimal.ONE);
         BigDecimal monthlyPayment = purchasePrice.multiply(numerator).divide(denominator);
         interestRate = interestRate.multiply(hundred);

         purchasePriceTextField.setText(currency.format(purchasePrice));
         downPaymentTextField.setText(currency.format(downPayment));
         interestRateTextField.setText(percent.format(interestRate));
         monthlyPaymentTextField.setText(currency.format(monthlyPayment));
      }
      catch (NumberFormatException ex) {
         purchasePriceTextField.setText("Enter amount");
         purchasePriceTextField.selectAll();
         purchasePriceTextField.requestFocus();
      }
   }

   // called by FXMLLoader to initialize the controller
   public void initialize() {
      // 0-4 rounds down, 5-9 rounds up 
      currency.setRoundingMode(RoundingMode.HALF_UP);
      
      // listener for changes to loanDurationSlider's value
      loanDurationSlider.valueProperty().addListener(
         new ChangeListener<Number>() {
            @Override
            public void changed(ObservableValue<? extends Number> ov, 
               Number oldValue, Number newValue) {
               loanDuration = newValue.intValue();
            }
         }
      );
   }
}

下面是我的FXML程序：

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.Slider?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.RowConstraints?>

<GridPane hgap="8.0" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" xmlns="http://javafx.com/javafx/8.0.60" xmlns:fx="http://javafx.com/fxml/1" fx:controller="MortgageCalculatorController">
   <columnConstraints>
      <ColumnConstraints halignment="RIGHT" hgrow="SOMETIMES" minWidth="10.0" />
      <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" />
   </columnConstraints>
   <rowConstraints>
      <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
      <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
      <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
      <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
      <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
   </rowConstraints>
   <children>
      <Label text="Purchase Price" />
      <Label fx:id="loanDurationLabel" text="10" GridPane.rowIndex="1" />
      <Label text="Loan Duration" GridPane.rowIndex="2" />
      <Label text="Down Payment" GridPane.rowIndex="3" />
      <Label text="Interest Rate" GridPane.rowIndex="4" />
      <Label text="Monthly Payment" GridPane.rowIndex="5" />
      <TextField fx:id="purchasePriceTextField" GridPane.columnIndex="1" />
      <TextField fx:id="loanDurationTextField" editable="false" focusTraversable="false" GridPane.columnIndex="1" GridPane.rowIndex="2" />
      <TextField fx:id="downPaymentTextField" GridPane.columnIndex="1" GridPane.rowIndex="3" />
      <TextField fx:id="interestRateTextField" GridPane.columnIndex="1" GridPane.rowIndex="4" />
      <TextField fx:id="monthlyPaymentTextField" editable="false" focusTraversable="false" GridPane.columnIndex="1" GridPane.rowIndex="5" />
      <Slider fx:id="loanDurationSlider" blockIncrement="10.0" max="30.0" value="10.0" GridPane.columnIndex="1" GridPane.rowIndex="1" />
      <Button maxWidth="1.7976931348623157E308" mnemonicParsing="false" onAction="#calculateButtonPressed" text="Calculate" GridPane.columnIndex="1" GridPane.rowIndex="6" />
   </children>
   <padding>
      <Insets bottom="14.0" left="14.0" right="14.0" top="14.0" />
   </padding>
</GridPane>

最后是错误列表：

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$FXHelper.main(LauncherHelper.java:873)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$1(LauncherImpl.java:182)
    at java.lang.Thread.run(Thread.java:748)
Caused by: javafx.fxml.LoadException: 
/C:/Users/EdenFlorian/Documents/Eclipse%20Workspace/COMP%20SCI%20316%20-%20Week%205%20Assignment/bin/MortgageCalculator.fxml:12

    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 MortgageCalculator.start(MortgageCalculator.java:13)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$8(LauncherImpl.java:863)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$7(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl.lambda$null$5(PlatformImpl.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$6(PlatformImpl.java:294)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$4(WinApplication.java:186)
    ... 1 more
Caused by: java.lang.NullPointerException
    at MortgageCalculatorController.<init>(MortgageCalculatorController.java:43)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at java.lang.Class.newInstance(Class.java:442)
    at sun.reflect.misc.ReflectUtil.newInstance(ReflectUtil.java:51)
    at javafx.fxml.FXMLLoader$ValueElement.processAttribute(FXMLLoader.java:927)
    at javafx.fxml.FXMLLoader$InstanceDeclarationElement.processAttribute(FXMLLoader.java:971)
    at javafx.fxml.FXMLLoader$Element.processStartElement(FXMLLoader.java:220)
    at javafx.fxml.FXMLLoader$ValueElement.processStartElement(FXMLLoader.java:744)
    at javafx.fxml.FXMLLoader.processStartElement(FXMLLoader.java:2707)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2527)
    ... 17 more
Exception running application MortgageCalculator

如果我需要提供任何进一步的信息，请告诉我。

试着摆脱

private int loanDuration = Integer.parseInt(loanDurationTextField.getText());

然后替换

BigDecimal numerator = interestRate.multiply(interestRate.add(BigDecimal.ONE).pow(loanDuration*12));
BigDecimal denominator = interestRate.add(BigDecimal.ONE).pow(loanDuration*12).subtract(BigDecimal.ONE);

与

更新以回答评论 你应该可以做一些类似的事情

loanDurationSlider.valueProperty().addListener(
    new ChangeListener<Number>() {
        @Override
        public void changed(ObservableValue<? extends Number> ov, Number oldValue, Number newValue) 
        {
            loanDurationTextField.setText(newValue.intValue().toString()));//or loanDurationTextField.setText(Integer.toString(newValue.intValue())); if intValue().toString() is not valid.
        }
     }
);

---

LoandrationTextField.getText似乎在LoandrationTextField初始化之前被调用。我会称之为内心的空虚，即使那没有意义；当调用initialized时，用户将没有机会在文本字段中键入任何内容。@James\D至少不会NullPointerException@JockX不，将改为NumberFormatException。。。这真的是一个很大的改进。去掉私有的int-loandration=Integer.parseIntloandrationTextField.getText；。当需要进行计算时，只需使用Integer.parseIntloAndrationTextField.getText。但是，我该如何处理滑块呢？public void changedobservablevalue我认为绑定到两个是最好的，但我不擅长绑定。我需要开始绑定更多。对于您的更新：new\u p到底应该是什么？我不理解您的问题。new\u p是一个数字。这就是你要问的吗？

loanDurationSlider.valueProperty().addListener(
    new ChangeListener<Number>() {
        @Override
        public void changed(ObservableValue<? extends Number> ov, Number oldValue, Number newValue) 
        {
            loanDurationTextField.setText(newValue.intValue().toString()));//or loanDurationTextField.setText(Integer.toString(newValue.intValue())); if intValue().toString() is not valid.
        }
     }
);