How to create Arraylist with 3 columns (Java)?

Question

I need some help, I'm new to java, so probably I will have to change a lot of things. I'm having this result:

[Goya, Scoop 2000 W, 123]

And if I try to add more, it will display:

[HMI, Scoop 2000 W, 123]
[HMI, Scoop 2000 W, 123, Fresnel, Set light 1000 W De Sisti, 124]
[HMI, Scoop 2000 W, 123, Fresnel, Set light 1000 W De Sisti, 124, Goya, Set light 1000 W De Sisti, 456]

And what I actually need is something like that:

[HMI, Scoop 2000 W, 123,]
[Fresnel, Set light 1000 W De Sisti, 124]
[Goya, Set light 1000 W De Sisti, 456]

Here is my code:

Component[] componente = painelMain.getComponents();
    list = new ArrayList();
    for (int i = 0; i < componente.length; i++) {
        if (componente[i] instanceof JTextField) {
            JTextField textfield = (JTextField) componente[i];
            if (!"".equals(textfield.getText())) {
                list.add(textfield.getText());
                System.out.println(list);
            }
        } else if (componente[i] instanceof JComboBox) {
            JComboBox combo = (JComboBox) componente[i];
            if (!"".equals(combo.getSelectedItem())) {
                list.add(combo.getSelectedItem());
            }
        }
    }
}

It sounds like you should be creating a new type to represent that combination of three values... (We can't really tell what they mean at the moment...) — Jon Skeet
– Jon Skeet, Commented Sep 5, 2015 at 21:23

Dici · Accepted Answer · 2015-09-05 21:31:04Z

What you want is a matrix. You can either use an array of type String[][] or a list of type List<List<String>>.

I also simplified your code (use of generics, factored out logic), however all these casts and intanceof are probably the sign of a bad design you should improve.

Component[] components = painelMain.getComponents();
List<List<String> list = new ArrayList<>();
List<String> line;

int i = 0, numCols = 3;
for (Component component : components) {
    if (i % numCols == 0) {
        line = new ArrayList<>();
        list.add(line);
    }
    String content = "";
    if (component instanceof JTextField) {
        content = ((JTextField) component).getText();            
    } else if (component instanceof JComboBox) {
        content = ((JComboBox<String>) component).getSelectedItem();
    }

    if (!content.isEmpty()) {
        line.add(content);
    }
    i = (i + 1) % 3;
}

There's an edge case if one of the strings gets empty, I don't know how you want to handle it.

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