Question

In my Swing application, the user must insert numbers and values, before switching to the next window. Now as a clean program should, I check every input if its valid or not, and if not, an error message is displayed and the next window does not open.

The structure of this check is as following (example):

Button buttonToOpenNextWindow = new JButton("next");
button.addActionListener(new ActionListener(){

    public void actionPerformed(ActionEvent e){
        if(checkValidty){
            // (...)
            new WindowA();
            frame.dispose(); // (*)
        }
    }
});

(*) Note: I know that the principle of multiple JFrames is ugly, and I’m on to change that, but for this question it’s irrelevant.

Now the focus of this question is this checkValidity(), which I structured like this:

private boolean checkValidity(){

    // check input 1
    try{
        Integer.parseInt(textField1.getText());
    }catch (NumberFormatException e){
        new ErrorDialog("input 1 is invalid!"); // own implemented dialog
        return false;
    }

    // check input 2
    try{
        Integer.parseInt(textField2.getText());
    }catch (NumberFormatException e){
        new ErrorDialog("input 2 is invalid!"); // own implemented dialog
        return false;
    }

    // (...)

    // check input n
    try{
        Integer.parseInt(textField_n.getText());
    }catch (NumberFormatException e){
        new ErrorDialog("input n is invalid!"); // own implemented dialog
        return false;
    }
    return true;
}

This works exactly as I want, BUT the code itself is very ugly, because having multiple input options the method gets 200, 300 or more lines long (as I do not only check if e.g. it’s a number, but also if the number makes sense in context of the program logic and so on). Is there a Swing -own method to check such things? Or has anyone a better idea how to realize exactly this functionality with split methods?

Answer 1

One solution would be to use Swing’s InputVerifier to validate input for every JTextField used. As the validation functionality is the same for each field, a single instance could be used for all components:

public class MyNumericVerifier extends InputVerifier {
    @Override
    public boolean verify(JComponent input) {
       String text = ((JTextField) input).getText();
       try {
          Integer.parseInt(text);
       } catch (NumberFormatException e) {
          return false;
       }

       return true;
    }
}

InputVerifier verifier = new MyNumericVerifier()
textField1.setInputVerifier(verifier);