Java-Swing: Can't trap user into typing a correct filename

Question

I'm trying to trap a user into typing a correct file name unless he presses cancel or X. But if he does cancel the input my program throws a NullPointerException.

public void openSaveAsDirectory() {

    JDialog dialog = new JDialog();
    dialog.setTitle("Save file as");
    String name = JOptionPane.showInputDialog(adTable, "Please type a name for your file");
    if(name != null && !name.isEmpty()) {

        File fileName = new File(SAVE_LOCATION + FILE_SEPERATOR + name + FILE_SUFFIX);
        book.saveUser(fileName);

    }

    while(name.isEmpty()) {
            name = JOptionPane.showInputDialog(adTable, "Please type a name for your file");
    }
}

Well, if they cancel your input dialog, `name` will be null. You do `while (name.isEmpty()) {`. `name` could be null. — nbokmans, Sep 27 '17 at 12:48
Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — nbokmans, Sep 27 '17 at 12:49
Just curious: why are you using JOptionPane vs. JFileChooser? — ControlAltDel, Sep 27 '17 at 12:51
@ControlAltDel no real reason. would it be better to use JFileChooser? — lucas6198, Sep 27 '17 at 12:55
@nbokmans Possibly a stupid question but if a user cancels the dialog and name is null would't it just do nothing? — lucas6198, Sep 27 '17 at 12:56
@lucas6198 JFileChooser would definitely get you a file. Getting a file from a file path that the user provided is not safe to always return a valid file. — Tobias Geiselmann, Sep 27 '17 at 12:56
@lucas6198 If name is null, then you try to evaluate null.isEmpty(). That's not possible. — Tobias Geiselmann, Sep 27 '17 at 12:57

Tobias Geiselmann · Accepted Answer · 2017-09-27T13:07:16.887

0

Based on your comment, here is an updated version that asks for an input as long as it is empty but stops, when the user hits the cancel button.

String name;
do {
    name = JOptionPane.showInputDialog(null, "Please type a name for your file");
    if(name == null) { //user hit cancel, break the loop
        break;
    }
} while(name.isEmpty());

edited Sep 27 '17 at 13:07

answered Sep 27 '17 at 12:52

Tobias Geiselmann

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Wouldn't this just trap a user forever? Because while name==null only occurs if the user presses cancel or X if I'm not mistaken. But I want the user to be able to cancel the input. – lucas6198 Sep 27 '17 at 13:00
Correct, that would keep asking forever. You never stated that you want it to stop, when the user cancels (although it makes perfect sense!). – Tobias Geiselmann Sep 27 '17 at 13:03
My fault I'm not good at expressing myself in english :/ I want him to be able to cancel the input. – lucas6198 Sep 27 '17 at 13:06

Java-Swing: Can't trap user into typing a correct filename

1 Answers1