Question

我正在写一个货币转换器，但我在计算每种货币的汇率方面遇到了一些麻烦。基本上我希望用户先选择一个货币，然后输入一个金额，然后按“开始”按钮计算费率。但是我在JMenuItem和JButton的听众遇到了麻烦。我已经为menuItem和JButton声明了两个监听器。我如何使用按钮上的监听器来查看menuIten上的选择，以便进行正确的计算？

感谢。

CODE：

    private class selectionListener implements ActionListener
    {
        double EuroToSterling(double euro)
        {
            double total = Double.parseDouble(amountField.getText());
            return total;
        }
        public void actionPerformed(ActionEvent e)
        {
            if (e.getActionCommand().equals("Euros"))
               // result = EuroToSterling(10*euro);
                currencyMenu.setLabel("Euros");
               // answerLabel.setText("this" + EuroToSterling(1.22*2));

            if (e.getActionCommand().equals("Japanese Yen"))
                currencyMenu.setLabel("Japanese Yen");

        }
    }



    private class GoButtonListener implements ActionListener
    {
        public void actionPerformed(ActionEvent evt)
        {

//please help with this section

Answer 1

通常的方法是菜单监听器改变应用程序的状态（即调用一个方法来保存字段中的汇率）。

然后计算代码可以读取该值并使用它。

Answer 2

用欧元试试吧。应该给你一个入门的地方。


/*
 *
 * Currency converting
 *
 */

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JButton;
import javax.swing.JTextField;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import javax.swing.JComboBox;

import javax.swing.UIManager;

public class CurrencyConverterWin extends JFrame {

    private JLabel promptLabel;
    private JTextField amountField;
    private JButton goButton;
    private JPanel inputPanel;
    private JPanel answerPanel;
    private JLabel answerLabel;
    private JLabel selectLabel;
    private JComboBox currencyMenuBar;
    private JPanel menuPanel;
    private double result = 0.0;
    private double euro = 1.22257;
    private double japYen = 152.073;
    private double rusRuble = 42.5389;
    private double usd = 1.5577;

    public CurrencyConverterWin() {
        super();
        this.setSize(500, 200);
        this.setTitle("Currency Converter Window");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        this.setLayout(new GridLayout(3, 1));

        this.selectLabel = new JLabel("Select a currency to convert to: ", JLabel.RIGHT);
        this.answerLabel = new JLabel(" ", JLabel.CENTER);

        currencyMenuBar = new JComboBox(new String[]{"Euros","Japanese Yen","Russian Rubles","US Dollars"});

        this.menuPanel = new JPanel();
        this.menuPanel.add(this.selectLabel);
        this.menuPanel.add(this.currencyMenuBar);
        this.add(this.menuPanel);

        this.promptLabel = new JLabel("(select a currency first) ", JLabel.RIGHT);
        this.answerLabel = new JLabel(" ", JLabel.CENTER);

        this.amountField = new JTextField("", 8);
        this.goButton = new JButton("GO");
        goButton.addActionListener(new java.awt.event.ActionListener() {

            public void actionPerformed(java.awt.event.ActionEvent evt) {
                buttonClicked(evt);
            }
        });

        this.inputPanel = new JPanel();
        this.inputPanel.add(this.promptLabel);
        this.inputPanel.add(this.amountField);
        this.inputPanel.add(this.goButton);

        this.add(this.inputPanel);

        this.answerPanel = new JPanel();
        this.answerPanel.add(this.answerLabel);
        this.add(this.answerPanel);
    }

    double EuroToSterling() {
        double total = Double.parseDouble(amountField.getText()) * euro;
        return total;
    }

    double JapYenToSterling()
    {
        double japToSterlingTotal = Double.parseDouble(amountField.getText()) * japYen;
        return japToSterlingTotal;
    }


//String currencyEntered = yearField.getText();
    public void buttonClicked(ActionEvent evt) {
        if(currencyMenuBar.getSelectedItem().equals("Euros"))
        {
            answerLabel.setText(EuroToSterling() + " Euros");
        }
        if(currencyMenuBar.getSelectedItem().equals("Japanese Yen"))
        {
            answerLabel.setText(JapYenToSterling() + " Japanese Yen");
        }
    }

    public static void main(String[] args) {        
        try{UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");}
        catch (Exception e){e.printStackTrace();}
        CurrencyConverterWin win = new CurrencyConverterWin();
        win.setVisible(true);
    }
}

Answer 3

我个人会添加一个Enumeration来表示货币转换类型。例如：

public enum ConversionType {
   DOLLARS,
   EUROS,
   RUBLES
   //ETC...
}

使用此功能，您可以在类中保留状态变量：

private ConversionType fromType;

这是您在选择侦听器中设置的内容。

从那里开始，基于状态变量（fromType）在动作监听器中进行不同的转换。像这样：

if( fromType== EUROS ) {
 convertEurosToSterling( value1, value2 );
}

这是一种通用方法 - 我希望这会有所帮助。

Answer 4

我还建议您使用JComboBox来存储货币。您将创建一个对象来存储货币名称和转换率。然后，当您需要计算转换金额时，您将从组合中获取所选项目并在计算中使用其转换率。使用这种方法，您可以轻松扩展您支持的货币数量。

查看：How to use Map element as text of a JComboBox以获取一个示例，让您开始使用组合框中的对象。

JAVA：如何在JMenuItem和Jbutton上使用侦听器来计算速率

4 个答案: