Local variables from a inner class must be final or effectively final

Question

JComboBox[] ChooseType = new JComboBox[a];
    JRadioButton[] Primary = new JRadioButton[a];
    ButtonGroup group = new ButtonGroup();
    for (int b = 0; b < a; b++) {
        ChooseType[b] = new JComboBox(Types);
        Primary[b] = new JRadioButton();
        group.add(Primary[b]);
        Primary[b].addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                ChooseType[b].setSelectedIndex(8);//Error here
            }
        });
    }

I already tried this:

final JComboBox[] ChooseType = new JComboBox[a];

I tried also to create a inner class and a method, so I dont have to deal directly with the JComboBox inside the actionPerformed. Can someone tell me how to fix it?

Did you look at any of the numerous duplicates with the exact same problem? — tnw, May 31 '17 at 14:57
Possible duplicate of [Problems with local variable scope. How to solve it?](https://stackoverflow.com/questions/25894509/problems-with-local-variable-scope-how-to-solve-it) — Frakcool, May 31 '17 at 14:58

score 1 · Accepted Answer · answered May 31 '17 at 14:58

1

The problem is with the b variable. You can use a temporary variable:

for (int b = 0; b < a; b++) {
  int b0 = b;
  chooseType[b] = new JComboBox(Types);
  //...
  chooseType[b0].setSelectedIndex(8);//Error here

ps: I've changed the capitalisation of the variable to match Java's conventions.

answered May 31 '17 at 14:58

assylias

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That was so simple. Thanks – May 31 '17 at 15:04

score 0 · Answer 2 · answered May 31 '17 at 14:58

To simply put it in code:

    JComboBox[] ChooseType = new JComboBox[a];
    JRadioButton[] Primary = new JRadioButton[a];
    ButtonGroup group = new ButtonGroup();
    for (int b = 0; b < a; b++) {
        //This is the item that's not final
        ChooseType[b] = new JComboBox(Types);
        Primary[b] = new JRadioButton();
        group.add(Primary[b]);
        final JComboBox forListener = ChooseType[b];
        Primary[b].addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                forListener.setSelectedIndex(8);//Fixed.
            }
        });
    }

Local variables from a inner class must be final or effectively final

2 Answers2