java array of arraylists

Question

I have four columns of buttons in my program. Buttons move between columns when assigned new ones. Instead of declaring 4 separate arraylists to store the buttons, is there a way to create 1 array of arraylists so I can simply itterate through the array?

I've tried List<JButton>[] lists = new ArrayList<JButton>[5];

But that won't work. What am I missing?

EDIT:

for(int i = 0; i < 5; i++){
            if(choiceList.getSelectedIndex() == i){
                if(btnPersons[nameList.getSelectedIndex()].getX() == column[i]){
                    JOptionPane.showMessageDialog(null, "Error - Name already present in the column.","", 1);
                }else{
                    for(int j = 0; j < 5; j++){
                        if(lists[j].get(i) != null){
                            lists[j].remove(btnPersons[nameList.getSelectedIndex()]);
                        }
                    }
                    lists[i].add(btnPersons[nameList.getSelectedIndex()]);
                    lists[i].get(i).setBounds(column[i], ROWS[i], 125, 20);
                    //reloadLocations();
                }
            }
        }

This is my code currently.Once a new column is selected it checks to see which listthe button was in and removes it, then adds it to the new list. But my new problem is that using lists[i] will no longer work. Idk how to properly loop through my list of arraylists using this declaration:

List<ArrayList<JButton>> lists = new ArrayList<ArrayList<JButton>>(); 

Answer 1

You have to keep a list of lists of JButton objects:

List<List<JButton>> lists = new ArrayList<List<JButton>>();
// populate (replace with your code)
lists.add(Arrays.asList(new JButton("list 1, button 1"), new JButton("list 1, button 2")));
lists.add(Arrays.asList(new JButton("list 2, button 3"), new JButton("list 2, button 4")));
lists.add(Arrays.asList(new JButton("list 3, button 5"), new JButton("list 3, button 6")));
lists.add(Arrays.asList(new JButton("list 4, button 7"), new JButton("list 4, button 8")));

// iterate
for(List<JButton> subList : lists) {
    for(JButton button : subList) {
        System.out.println(button.getText());
    }
}

Answer 2

Giving an example of what worked for me / talked above.

    List []oArrayOfArrayList = new ArrayList[2];

    List<String> oStringList = new ArrayList<String>();
    List<Integer> oIntegerList = new ArrayList<Integer>();

    oArrayOfArrayList[0] = oStringList ;
    oArrayOfArrayList[1] = oIntegerList ;

Answer 3

You cannot create arrays from classes with generic parameters.

You'll either want to make a list of a list, or forgo generic parameters.

Answer 4

您无法为泛型对象调用 new 运算符，因为在运行时该类型已被擦除。

Answer 5

create a class for your ArrayList:

    private class xxx extends ArrayList<JButton> {
        // need serial to keep IDE happy
        private static final long serialVersionUID = -2392107594926751233L;
    };

    private xxx[] lists = new xxx[5];