Clear all text fields of java swing form at program start

Question

As a beginner in java programming working in netbeans IDE, I made a currency converter; I have a textfield for 'franc' and another one for 'euro', a clear button for clearing both text fields, a convert button and a quit button to leave the window. I added code behind convert button so that the conversion should be performed when it is pressed. Then i'm having some issue: When I run the program and enter a value to convert, the conversion doesn't happen unless I first click the clear button and then input the value. Now my question is how can I prevent the program from doing that. Or if it is not possible to do so, is there a way I can automatically clear all the text fields at the program start? Thanks for helping

Here are the codes that handle events in the program

~ private void   clear_buttonActionPerformed(java.awt.event.ActionEvent evt) {                                             
        euro_field.setText(" ");
        franc_field.setText(" ");
}                                            

private void quit_buttonActionPerformed(java.awt.event.ActionEvent evt) {                                            
    System.exit(0);
}                                           

private void convert_buttonActionPerformed(java.awt.event.ActionEvent evt) {                                               
    double francVal, euroVal;
    String a = franc_field.getText();
    String b = euro_field.getText();
    if(b.equals(" ") && !a.equals(" ")) {
        francVal = Double.parseDouble(franc_field.getText());
        euroVal = francVal/660.85;
        euro_field.setText(String.valueOf(euroVal));
    }
    else if(a.equals(" ") && !b.equals(" ")) {
        euroVal = Double.parseDouble(euro_field.getText());
        francVal = euroVal*660.85;
        franc_field.setText(String.valueOf(francVal));
    }
}   

 // Variables declaration - do not modify                     
private java.awt.Button clear_button;
private java.awt.Button convert_button;
private javax.swing.JTextField euro_field;
private java.awt.Label euro_label;
private javax.swing.JTextField franc_field;
private java.awt.Label franc_label;
private java.awt.Button quit_button;
private java.awt.Label welcome_label;
// End of variables declaration ~    

Answer 1

When a JTextField is empty, its getText() method returns an empty string and not a string that contains a single space. Hence the conditions in method convert_buttonActionPerformed() are never true, but method clear_buttonActionPerformed() actually inserts a single space into the JTextField so when you call method convert_buttonActionPerformed() after calling method clear_buttonActionPerformed() then the conditions in method convert_buttonActionPerformed() are true.

Change method clear_buttonActionPerformed() to the following:

private void clear_buttonActionPerformed(java.awt.event.ActionEvent evt) {                                             
    euro_field.setText("");
    franc_field.setText("");
}

And change method convert_buttonActionPerformed() to the following:

private void convert_buttonActionPerformed(java.awt.event.ActionEvent evt) {                                               
    double francVal, euroVal;
    String a = franc_field.getText();
    String b = euro_field.getText();
    if(b.equals("") && !a.equals("")) {
        francVal = Double.parseDouble(franc_field.getText());
        euroVal = francVal/660.85;
        euro_field.setText(String.valueOf(euroVal));
    }
    else if(a.equals("") && !b.equals("")) {
        euroVal = Double.parseDouble(euro_field.getText());
        francVal = euroVal*660.85;
        franc_field.setText(String.valueOf(francVal));
    }
}