Java：将ArrayList与JComboBox和JTextField结合使用

Question

I am currently trying to create a GUI which is fed information from a .txt file which contains exchange rates.

The text file contains 3 different values which are separated with a ','.

The values are: Currency Name, Exchange Rate, Currency Symbol.

I have the program working so that it stores these 3 values into 3 different ArrayLists

The program also updates the JComboBox with the Currency Name.

However, I now need the program to select the correct Exchange Rate and Currency Symbol based on what Currency Name the user has chosen in the JComboBox.

For example, if the user picks USD (arrayCurrency) and inputs 5 into the JTextField the program needs to chose the correct Exchange Rate (arrayRate).

Answer 1

However, I now need the program to select the correct Exchange Rate and Currency Symbol based on what Currency Name the user has chosen in the JComboBox.

This isn't exactly a question... I'm assuming you're asking for the following:

How do I get the value from a JComboBox? -> yourJCBox.getSelectedItem();

Now that you have this String - you need to decide how to map the exchange rates to the dollar amounts. Whether it be 2d, 3d arrays, or an object of your devising:

public class myCurrency() {
  String currnecy;
  String symbol;
  Double rate;

  public myCurrency(String c, String s, Double r) {
    // Constructor stuff
  }

  // Getters and setters
}

Now you have idea for everything you need to do to check if some currency selected should be displayed with some exchange rate and some symbol.

Answer 2

You can manage it easily by:

1. Creating a Currency class (datatype)
2. Storing the currencies in a Map instead of a List

Given below is the sample code:

import java.util.HashMap;
import java.util.Map;

class Currency {
    String code;
    double convertionRate;
    String symbol;

    Currency(String code, double convertionRate, String symbol) {
        this.code = code;
        this.convertionRate = convertionRate;
        this.symbol = symbol;
    }

    public double getConvertionRate() {
        return convertionRate;
    }

    public void setConvertionRate(double convertionRate) {
        this.convertionRate = convertionRate;
    }

    public String getSymbol() {
        return symbol;
    }

    public void setSymbol(String symbol) {
        this.symbol = symbol;
    }
}

public class Main {
    public static void main(String[] args) {
        Map<String, Currency> currencyMap = new HashMap<String, Currency>();
        // Populate currencyMap with values read from the .txt file e.g.
        currencyMap.put("USD", new Currency("USD", 1.60, "$"));
        // Replace the above line with currencyMap.put(currency_code-from-file,new
        // Currency(currency_code-from-file,conversion_rate-from-file,currency_symbol-from-file));
        // and use it inside the loop which you must be using to read the content from .txt file

        // Getting the corresponding conversion rate and symbol for a currency e.g. USD
        Currency currency = currencyMap.get("USD");
        // Replace the above statement with Currency
        // currency=currencyMap.get(String.valueOf(JComboBox.getSelectedItem()) in your
        // program.
        double convertionRate = currency.getConvertionRate();
        String symbol = currency.getSymbol();
        // Use convertionRate and symbol in your calculation
    }
}

Update: Since you have mentioned in your comment that you are facing difficulty loading the currencies into currencyMap , I have added the following update just to demonstrate how to load the currencies from the .txt file into currencyMap :

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

class Currency {
    String code;
    double convertionRate;
    String symbol;

    Currency(String code, double convertionRate, String symbol) {
        this.code = code;
        this.convertionRate = convertionRate;
        this.symbol = symbol;
    }

    public double getConvertionRate() {
        return convertionRate;
    }

    public void setConvertionRate(double convertionRate) {
        this.convertionRate = convertionRate;
    }

    public String getSymbol() {
        return symbol;
    }

    public void setSymbol(String symbol) {
        this.symbol = symbol;
    }
}

public class Main {
    Map<String, Currency> currencyMap = new HashMap<String, Currency>();

    public static void main(String[] args) {
        Main main = new Main();
        main.populateCurrencyMap();

        // Getting the corresponding conversion rate and symbol for a currency e.g. USD
        Currency currency = main.currencyMap.get("USD");
        if (currency != null)
            System.out.println("Rate: " + currency.getConvertionRate() + ", Symbol: " + currency.getSymbol());
    }

    void populateCurrencyMap() {
        File file = new File(
                "/Users/arvind.avinash/Documents/workspace-spring-tool-suite-4-4.4.0.RELEASE/AdHoc/src/currency2.txt");
        try {
            BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream(file), "UTF8"));

            String line = in.readLine().trim();

            while (line != null) {
                String[] parts = line.split(",");
                String currency = parts[0].trim();
                double rate = Double.parseDouble(parts[1].trim());
                String symbol = parts[2].trim();

                currencyMap.put(currency, new Currency(currency, rate, symbol));
                line = in.readLine();
            }

            in.close();

        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
}

Output:

Rate: 1.6, Symbol: $

Content of currency2.txt:

USD, 1.60, $
EUR, 1.41, €