JComboBoxes的ArrayList

Question

I created an ArrayList of JComboBox

private static ArrayList<JComboBox> comboList = new ArrayList<>();

and then added each instance of JComboBox to the ArrayList

private void courseUnit() {
        String[] units = {"6", "5", "4", "3", "2", "1"};
        int x = 520, y = 30;
        for (int i = 0; i < 10; i++) {
            comboUnits = new JComboBox<>(units);
            comboUnits.setBounds(x, y, 100, 25);
            y += 30;
            comboUnits.setToolTipText("Select course unit");
            comboUnits.setVisible(true);
            comboUnits.addActionListener(new PaneAction());
            add(comboUnits);
            comboList.add(comboUnits); //comboUnits added to ArrayList
        }
    }

My question is, how do i get the selectedItem from each comboBox in the ArrayList because i tried this

//this is supposed to get the selected item of the first ComboBox and assign to courseGrade[0]
    public void actionPerformed(ActionEvent evt) {
            String[] courseGrade = new String[10];
            courseGrade[0] = (String)comboList.get(0).getSelectedItem();

and the program didn't compile.

Answer 1

You can should attach ActionListner while you are adding the JComboBox to the ArrayList

    private void courseUnit() {
            String[] units = {"6", "5", "4", "3", "2", "1"};
            int x = 520, y = 30;
            for (int i = 0; i < 10; i++) {
                comboUnits = new JComboBox<>(units);
                comboUnits.setBounds(x, y, 100, 25);
                y += 30;
                comboUnits.setToolTipText("Select course unit");
                comboUnits.setVisible(true);
                //comboUnits.addActionListener(new PaneAction());
                add(comboUnits);

//////////////// Here are the changes

                comboUnits.addActionListener (new ActionListener () {
                   public void actionPerformed(ActionEvent e) {
                      String selectedItem = (String)e.getSelectedItem();
                   }
                });
                comboList.add(comboUnits); //comboUnits added to ArrayList
            }
        }

Answer 2

I finally got it. I had to create the ArrayList as a static instance variable

private static ArrayList<JComboBox> comboList;

and then instantiated it in the constructor

comboList = new ArrayList<>();

The new courseUnit() method now looks like this

private void courseUnit() {
        String[] units = {"6", "5", "4", "3", "2", "1"};
        int x = 520, y = 30;
        for (int i = 0; i < 10; i++) {
            comboUnits = new JComboBox<>(units);
            comboUnits.setBounds(x, y, 100, 25);
            comboUnits.setToolTipText("Select course unit");
            y += 30;
            comboUnits.setVisible(true);
            add(comboUnits);
            //I added ActionListener to each comboBox in the ArrayList,
            //thanks to Junaid for this
            comboUnits.addActionListener(new ActionListener(){
                public void actionPerformed(ActionEvent evt){    
                    ArrayList<String> courseGrade = new ArrayList<>();
                    JComboBox comboBox = (JComboBox) evt.getSource();
                    courseGrade.add((String) comboBox.getSelectedItem());
                }
            });
            comboList.add(comboUnits);
      }//end of loop
    } //end of method