从文件读取并用新数据填充现有的JComboBox

Question

I am attempting to write a conversion program in which a new file can be loaded in to the program and change the conversion (needs to also include validation if the file is corrupted). I currently have the conversions hard coded in and want to extend the program so that it accepts the conversion factors from an external txt file.

I am new to programming and don't really understand how to do this can someone help?

public class CurrencyPanel extends JPanel{

//Declaring global variables which include buttons, labels, comboBox and a CheckBox
    private final static String[] conversionList = { "Euro (EUR)", "US Dollers(USD)", "Australian Dollars (AUD)", 
                                            "Canadian Dollars (CAD)", "Icelandic Króna (ISK)", "United Arab Emirates Dirham (AED)", 
                                            "South African Rand (ZAR)", "Thai Baht (THB)"};
    private JTextField inputField;
    private JLabel labelOutput, labelCount, labelReverse;
    private JCheckBox reverseCheck;
    private JComboBox<String> comboSelect;
    private int count = 0;


    public MainPanel mainPanel;

CurrencyPanel() {

    //initialising the convertListner to listener
            ActionListener listener = new ConvertListener();

            //setting comboBox to variable of list of conversions
            comboSelect = new JComboBox<String>(conversionList);
            comboSelect.setToolTipText("Select Conversion Type"); //ToolTip

            JLabel labelEnter = new JLabel("Enter value:"); //enter value label


            JButton convertButton = new JButton("Convert"); //convert button
            convertButton.addActionListener(listener); // convert values when pressed
            convertButton.setToolTipText("Press to convert value"); //ToolTip

            JButton clearButton = new JButton ("Clear"); //clear button
            clearButton.addActionListener(new ClearLabel()); //clear labels when button pressed
            clearButton.setToolTipText("Press to Clear Value & Conversion Counter"); //ToolTip

            labelOutput = new JLabel("---"); //label to be changed when conversion done
            inputField = new JTextField(5); //textField for the user to input
            inputField.addActionListener(listener); //Press return to do conversion
            labelOutput.setToolTipText("Conversion Value"); //ToolTip
            inputField.setToolTipText("Enter the value you wish to convert"); //ToolTip

            labelCount = new JLabel("Conversion Count: 0"); //Conversion count label to be changed when conversion occurs
            labelCount.setToolTipText("Amount of conversions made"); //ToolTip

            labelReverse = new JLabel("Reverse Conversion"); //ReverseConversion label
            reverseCheck = new JCheckBox(); //new CheckBox
            reverseCheck.setToolTipText("Check the box to reverse the conversion type"); //ToolTip

            //adding components to the panel
            add(comboSelect);
            add(labelEnter);
            add(inputField);
            add(convertButton);
            add(labelOutput);


            //setting size and colour of panel
            setPreferredSize(new Dimension(800, 100));
            setBackground(Color.cyan);

        }

            public void clearLabelMethod() {
                labelOutput.setText("---");
                inputField.setText("");
                count = 0;
                labelCount.setText("Conversion Count: 0");
            }




            //ActionListener to clear labels 
            private class ClearLabel implements ActionListener{
                @Override
                public void actionPerformed(ActionEvent e)
                {
                    labelOutput.setText("---");
                    inputField.setText("");
                    count = 0;
                    labelCount.setText("Conversion Count: 0");
                }
            }



        //ActionListener that does the main conversions
        private class ConvertListener implements ActionListener {


            @Override
            public void actionPerformed(ActionEvent event) {

                String text = inputField.getText().trim();

                //attempting to clear the combo box before repopulating
                comboSelect.removeAllItems();

                //try block to display message dialog
                try {   
                    Double.parseDouble(text); //checking to see if value is an double
                    if(inputField.getText().isEmpty()) 
                    { //if statement to check if inputField is empty


                    }
                }catch (Exception e) {
                    JOptionPane.showMessageDialog(null, "Please enter a valid number"); //message dialogue
                    return;
                }

                // if exception isn't thrown, then it is an integer
                if (text.isEmpty() == false) {

                    double value = Double.parseDouble(text); //converting double to string

                    // the factor applied during the conversion
                    double factor = 0;

                    // the offset applied during the conversion.
                    double offset = 0;

                    String symbol = null;


                    // Setup the correct factor/offset values depending on required conversion
                    switch (comboSelect.getSelectedIndex()) {

                    case 0: // Euro
                        factor = 1.359;
                        symbol = "€";
                        break;

                    case 1: // USD
                        factor = 1.34;
                        symbol = "$";
                        break;

                    case 2: // AUD
                        factor = 1.756;
                        symbol = "$";
                        break;

                    case 3: // CAD  
                        factor = 1.71;
                        symbol = "$";
                        break;

                    case 4: // ISK  
                        factor = 140.84;
                        symbol = "kr";
                        break;

                    case 5: // AED
                        factor = 4.92;
                        symbol = "د.إ";
                        break;

                    case 6: // ZAR  
                        factor = 17.84;
                        symbol = "R";
                        break;

                    case 7: // THB
                        factor = 43.58;
                        symbol = "฿";
                        break;
                    }


                    double result = 0;

                    if(mainPanel.reverseCheckMethod() == true) { //if the reverse check option is selected
                        result = value / factor - offset;   //do the opposite conversion

                    }else {
                        result = factor * value + offset; //if not then do regular conversion
                    }

                    DecimalFormat decFormat = new DecimalFormat("0.00"); //DecimalFormat of output
                    String formatted = decFormat.format(result); //formatting the result 2 decimal places

                    mainPanel.conCount();

                    labelOutput.setText(symbol+formatted); //setting the output label


                }
            }

        }

        public void loadFile() {

            int itemCount = comboSelect.getItemCount();
            for(int i=0;i<itemCount;i++) {
                comboSelect.removeAllItems();
            }

            try {
                BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("currency.txt"), "UTF8"));

                String line = null;

                while ((line = br.readLine()) != null) {
                     String[] values = line.split(",");

                     String currencyType = values[0];
                     String currencyValueTxt = values[1];
                     String currencySymbol = values[2];

                     Double conversionValue = Double.parseDouble(currencyValueTxt);

                     comboSelect.addItem(currencyType);

                     br.close();
                }

            }catch(Exception e) {
                JOptionPane.showMessageDialog(null, "File Error");
            }

        }
}

The currency file in question is encoded in UTF-8 and is as follows:

Euro (EUR), 1.41, €
US Dollars (USD), 1.24, $
Australian Dollars (AUD), 1.86, $
Bermudan Dollar (BMD), 1.35, $
Icelandic króna (ISK),  141.24, kr
United Arab Emirates Dirham (AED), 4.12, د.إ
South African Rand (ZAR), 16.84, R
Thai Baht (THB), 42.58, ฿

Answer 1

Well you want to start to use a custom object to hold related data.

So you would start by creating a Currency object with 3 properties:

1. Name
2. Rate
3. Symbol

Something like:

public class Currency
{
    private String name;
    private double rate;
    private String symbol;

    public Currency (String name, double rate, String symbol)
    {
        this.name = name;
        this.rate = rate;
        this.symbol = symbol;
    }

    // add getter methods here

    @Override
    public String toString()
    {
        return name;
    }
}

You would then need to add getter methods, getName(), getRate() and getSymbol() so you can access the data from the object.

Now you can add the "hard coded" currency objects to your combo box with code like:

//comboSelect = new JComboBox<String>(conversionList);
comboSelect = new JComboBox<Currency>();
comboSelect.addItem( new Currency("Euro (EUR)", 1.23, "€") );
comboSelect.addItem( new Currency("US Dollar (USD), 1.23, "$") );
...

The default renderer for the combo box will invoke the toString() method of your Currency object for the text to display in the combo box.

Now the ActionListener code for you combo box is greatly simplified:

Currency currency = (Currency)comboSelect.getSelectedItem();
factor = currency.getRate();
symbol = currency.getSymbol();

No need for the switch statement.

In your current design you have the names hard code in an Array and the rate/symbol hard coded in the ActionListener. With this design you have all the data together in a simple object.

So first get this basic logic working with hard coded Currency objects.

Then when you are ready to create dynamic currency objects your looping code would be something like:

while ((line = br.readLine()) != null) 
{
    String[] values = line.split(",");
    double rate = Double.parseDouble( values[1] );
    Currency currency = new Currency(values[0], rate, values[2]); 
    comboSelect.addItem( currency);

     //br.close(); you only close the file after reading all the lines of data
}

br.close();

Note: it really isn't a good idea to use the toString() method for the text to display in the combo box. Instead you should be using a custom renderer. Once you have gotten the above suggestions working you can check out: Combo Box With Custom Renderer for more information on this topic.