CODEWITHSUNDEEP
javaarraysimmutability
WesternGun
WesternGun

Reputation: 12728

Why my Array of JComboBox are not updated?

I create a field of Object[] named array:

private Object[] array;

And then I initiate it with dimension and add JComboBox into it in method A:

array = new Object[14];
array[0] = combo1;
array[1] = combo2;
....

Then, I changed the data model of these JComboBox in method B, changeCombo.

private JComboBox<String> changeCombo(String newOption, JComboBox<String> combo, Set<String> data) {
if (combo != null) {
    int size = combo.getModel().getSize();
    data.add(newOption);
    if (size != data.size()){
        combo = updateCombo(data);
    }
        return combo;
    }
}

Where updateCombo(data) is: 

private JComboBox<String> updateCombo(Set<String> dataSet) {
    JComboBox<String> combo = new JComboBox<String>();
    DefaultComboBoxModel<String> model = new DefaultComboBoxModel<>();
    model.insertElementAt(Constantes.COMBO_TEXT_TODOS, 0);
    for (String s: dataSet) {
        model.addElement(s);
    }
    combo.setModel(model);
    combo.setSelectedIndex(0);
    combo.addItemListener(new ComboItemListener());
    return combo;
}

At last, I invoke this array again in method C, only to find all JComboBox has no data in it.

for (int i=0; i<14; i++ ){
    TableColumn col = table.getColumnModel().getColumn(i);
    col.setCellEditor(new DefaultCellEditor((JComboBox<String>)(array[i])));
    //here I found the data collection in each combo is empty
    col.setCellRenderer(new ComboRenderer());
}

So, arrays are immutable in my case? Or these JComboBox are immutable?

Upvotes: 2

Views: 74

Answers (1)

Denys Kurochkin
Denys Kurochkin

Reputation: 1495

In the updateCombo you create a new instance of JComboBox, but the array contains a link to the old instances

You need to explicitly replace old instances to newer ones returned by changeCombo.
Something like this:

array[i] = changeCombo(newOption, array[i], data);

I think, In your case, it is better to reuse existing instance of combo - just change it's model to the newer one. Or more - modify existing model.

For example, you can replace updateCombo with updateComboModel:

private void replaceComboModel(JComboBox<String> combo, Set<String> dataSet) {
    DefaultComboBoxModel<String> model = new DefaultComboBoxModel<>();
    model.insertElementAt(Constantes.COMBO_TEXT_TODOS, 0);
    for (String s: dataSet) {
        model.addElement(s);
    }
    combo.setModel(model);
}

And just call replaceComboModel(combo, data) instead of combo = updateCombo(data) inside changeCombo

I may miss some swing internals,

This Oracle tutorial can also help you understand the nature of object references - see the Passing Reference Data Type Arguments part.

Upvotes: 1

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