Combo box in Java - nullpointer

Question

I am trying to add this list of Strings

private String[] dest = {"New York", "Dahab", "Rome", "Sydney", "Tokyo"};

To this combo box like so

    for(int i = 0; i < dest.length; i++){
        System.out.println(dest[i]);
        destinationField.addItem(dest[i]);
    }

However I get a NullPointerException on the destinationField.addItem(dest[i]); line

JComboBox<String> destinationField;

Is `destinationField` null? – resueman Aug 28 '14 at 14:26 — resueman, Aug 28 '14 at 14:26
and what is destinationField? – Kumar Abhinav Aug 28 '14 at 14:28 — Kumar Abhinav, Aug 28 '14 at 14:28
JComboBox destinationField; – user3456349 Aug 28 '14 at 14:29 — user3456349, Aug 28 '14 at 14:29

Bruno Franco · Answer 1 · 2014-08-28T14:35:14.280

3

Probably your destinationField is getting there in a null form, because otherwise, if the problem was the dest[i] you would have a nullpointer in the line System.out.println(dest[i]);.

Try this:

JComboBox<String> destinationField = new JComboBox<>();

Your reference destinationField was not pointing to a real object in memory, so when you tried to use it inside the for, it didn't have a real object in memory. So, the new word makes it, allocate a real object to memory.

edited Aug 28 '14 at 14:35

answered Aug 28 '14 at 14:29

Bruno Franco

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Worked, thank you! Can you explain what was wrong please as I dont get it. – user3456349 Aug 28 '14 at 14:32
1

Actually I understand, it gave null before because it was set to null? – user3456349 Aug 28 '14 at 14:33
I added an explanation on the post – Bruno Franco Aug 28 '14 at 14:35

Combo box in Java - nullpointer

1 Answers1