获取实时的货币汇率并进行在线换算

以下是一个JavaFX程序，它可以通过连接到公共API获取实时的货币汇率并进行在线换算。

import javafx.application.Application;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;
import java.util.*;

public class CurrencyConverter extends Application {

    private Map<String, Double> rates = new HashMap<>();

    @Override
    public void start(Stage primaryStage) throws Exception {
        GridPane gridPane = new GridPane();
        gridPane.setHgap(10);
        gridPane.setVgap(10);
        gridPane.setPadding(new Insets(10, 10, 10, 10));

        Label fromLabel = new Label("从：");
        ComboBox<String> fromComboBox = new ComboBox<>();
        fromComboBox.setEditable(false);
        fromComboBox.getItems().addAll("USD", "EUR", "GBP", "CNY", "JPY", "KRW", "AUD", "CAD", "CHF", "HKD");
        fromComboBox.getSelectionModel().selectFirst();
        gridPane.addRow(0, fromLabel, fromComboBox);

        Label toLabel = new Label("到：");
        ComboBox<String> toComboBox = new ComboBox<>();
        toComboBox.setEditable(false);
        toComboBox.getItems().addAll("USD", "EUR", "GBP", "CNY", "JPY", "KRW", "AUD", "CAD", "CHF", "HKD");
        toComboBox.getSelectionModel().selectLast();
        gridPane.addRow(1, toLabel, toComboBox);

        Label amountLabel = new Label("金额：");
        TextField amountTextField = new TextField();
        amountTextField.setPromptText("请输入要转换的金额");
        gridPane.addRow(2, amountLabel, amountTextField);

        Label resultLabel = new Label("转换结果：");
        Label resultValueLabel = new Label("");
        gridPane.addRow(3, resultLabel, resultValueLabel);

        Button convertButton = new Button("换算");
        convertButton.setOnAction(event -> {
            String fromCurrency = fromComboBox.getSelectionModel().getSelectedItem();
            String toCurrency = toComboBox.getSelectionModel().getSelectedItem();
            double amount = Double.parseDouble(amountTextField.getText().trim());

            double fromRate = rates.get(fromCurrency);
            double toRate = rates.get(toCurrency);
            double result = amount / fromRate * toRate;
            resultValueLabel.setText(String.format("%.2f %s = %.2f %s", 
                amount, fromCurrency, result, toCurrency));
        });
        gridPane.addRow(4, convertButton);

        Scene scene = new Scene(gridPane, 400, 200);
        primaryStage.setTitle("货币换算");
        primaryStage.setScene(scene);
        primaryStage.show();

        // 在JavaFX应用中使用线程
        Thread thread = new Thread(() -> {
            while(true) {
                try {
                    updateRates();
                    Thread.sleep(60000); // 每60秒更新一次汇率
                } catch (InterruptedException | IOException e) {
                    e.printStackTrace();
                }
            }
        });
        thread.setDaemon(true);
        thread.start();
    }

    private void updateRates() throws IOException {
        URL url = new URL("https://api.exchangeratesapi.io/latest");
        URLConnection connection = url.openConnection();
        connection.setRequestProperty("User-Agent", "Mozilla/5.0");

        try(BufferedReader reader = new BufferedReader(
                new InputStreamReader(connection.getInputStream(), "UTF-8"))) {
            String line;
            StringBuilder response = new StringBuilder();
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }

            String json = response.toString();
            rates.clear();
            rates.put("EUR", 1.0);
            Map<String, Object> map = new ObjectMapper().readValue(json, Map.class);
            Map<String, Double> ratesMap = (Map<String, Double>) map.get("rates");
            for (Map.Entry<String, Double> entry : ratesMap.entrySet()) {
                rates.put(entry.getKey(), entry.getValue());
            }
        }
    }

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

在该程序中，用户可以选择要转换的货币类型、输入要转换的金额，然后点击“换算”按钮进行在线换算。该程序每60秒更新一次实时汇率，保证换算的准确性。

在JavaFX应用程序中使用线程需要注意线程的执行顺序以及线程的安全性，避免出现UI界面卡死或者数据不一致的问题。