相关疑难解决方法(0)

使用什么方法返回用户选择的选择？

JPanel ageSelection = new JPanel();
JLabel age = new JLabel("Age:");

ArrayList<Integer> ageList = new ArrayList<Integer>();

for (int i = 1; i <= 100; ++i) {
    ageList.add(i);
}

DefaultComboBoxModel<Integer> modelAge = new DefaultComboBoxModel<Integer>();
for (Integer i : ageList) {
    modelAge.addElement(i);
}

JComboBox<Integer> ageEntries = new JComboBox<Integer>();
ageEntries.setModel(modelAge);

ageEntries.addActionListener(new putInTextListener());

ageSelection.add(age);
ageSelection.add(ageEntries);


class putInTextListener implements ActionListener {
    public void actionPerformed (ActionEvent event) {
        ageEntries.getSelectedItem();
    }
}

当添加最后一行(ageEntries.getSelectedItem();)时,我收到一个错误:

线程"AWT-EventQueue-0"中的异常java.lang.NullPointerException

有任何想法吗？

编辑代码:

class putInAgeListener implements ItemListener {
    public void itemStateChanged(ItemEvent e) …