private void Length() { tfD.setText(String.valueOf(Character.lengthCase(tfC.getText().charAt(0)))); } private void is FirstChar() { tfD.setText(String.valueOf(Character.firstCharCase(tfC.getText().charAt(0)))); } private void toUp() { tfD.setText(String.valueOf(Character.toUpperCase(tfC.getText().charAt(0)))); } private void toLow() { tfD.setText(String.valueOf(Character.toLowerCase(tfC.getText().charAt(0)))); } private void LastChar() { tfD.setText(String.valueOf(Character.lastCharCase(tfC.getText().charAt(0)))); } public static void main(String[] args) { launch(args); } }

在代码中，您需要修改以下两处错误：

1. `Length()` 方法中的 `Character.lengthCase()` 应改为 `Character.toString().length()`，用于获取字符串的长度。

2. `is FirstChar()` 方法中的 `is` 应该改为 `First`，即 `Character.firstCharCase()`，用于获取字符串的第一个字符。

修改后的代码如下：

package application;

import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;

public class AS3 extends Application {
    TextField tfA = new TextField();
    TextField tfB = new TextField();
    TextField tfC = new TextField();
    TextField tfD = new TextField();
    Button Length = new Button(" Length ");
    Button ToUp = new Button(" To Up");
    Button Tolow = new Button(" To low ");
    Button FirstChar = new Button(" First Char ");
    Button LastChar = new Button(" Last Char ");

    @Override
    public void start(Stage primaryStage) {
        GridPane gridPane = new GridPane();
        gridPane.setHgap(5);
        gridPane.setVgap(5);

        gridPane.add(new Label("Student ID:"), 0, 0);
        gridPane.add(tfA, 1, 0);
        gridPane.add(new Label("Name:"), 0, 1);
        gridPane.add(tfB, 1, 1);
        gridPane.add(new Label("A Character"), 0, 3);
        gridPane.add(new Label("="), 2, 3);
        gridPane.add(new Label("Result"), 5, 3);
        gridPane.add(tfC, 1, 4);
        gridPane.add(tfD, 5, 4);

        gridPane.setAlignment(Pos.CENTER);
        tfD.setAlignment(Pos.BOTTOM_RIGHT);

        HBox hBox = new HBox(Length, ToUp, Tolow, FirstChar, LastChar);
        hBox.setAlignment(Pos.CENTER);

        BorderPane borderPane = new BorderPane();
        borderPane.setCenter(gridPane);
        borderPane.setBottom(hBox);

        Length.setOnAction(e -> Length());
        ToUp.setOnAction(e -> toUp());
        Tolow.setOnAction(e -> toLow());
        FirstChar.setOnAction(e -> FirstChar());
        LastChar.setOnAction(e -> LastChar());

        Scene scene = new Scene(borderPane, 600, 400);
        primaryStage.setTitle("Jayce 201044");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private void Length() {
        tfD.setText(String.valueOf(tfC.getText().length()));
    }

    private void FirstChar() {
        tfD.setText(String.valueOf(tfC.getText().charAt(0)));
    }

    private void toUp() {
        tfD.setText(String.valueOf(Character.toUpperCase(tfC.getText().charAt(0))));
    }

    private void toLow() {
        tfD.setText(String.valueOf(Character.toLowerCase(tfC.getText().charAt(0))));
    }

    private void LastChar() {
        tfD.setText(String.valueOf(tfC.getText().charAt(tfC.getText().length() - 1)));
    }

    public static void main(String[] args) {
        launch(args);
    }
}