解析java中的dom错误(Parsing dom error in java)

 在您的SecondUI您正在创建OneUI新实例 
 
final OneUI obj = new OneUI();
obj.setVisible(true);// you don't call even this
 
 但是你不称之为真正可见的。所以有一个隐藏的jframe和combobox组合框被更新，但不是第一帧的组合框，并且你看不到更新的组合框，因为框架不可见 
 
 解决这个传递给secondui的oneui引用然后调用那个引用的方法 
 
 例如OneUI.java 
 
public class OneUI extends JFrame {

    private JPanel contentPane;
    private JComboBox comboBox;
    private DefaultComboBoxModel modeltest;
    private Integer count = 0;
    private JButton btnOpenSecondUi;
    private SecondUI secondui;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            public void run() {
                OneUI frame = new OneUI();
                frame.setVisible(true);
            }
        });
    }

    public OneUI() {

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        JButton btnAddOne = new JButton("Add 1 element");
        btnAddOne.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                updateModelCmb();
            }
        });
        btnAddOne.setBounds(187, 46, 129, 23);
        contentPane.add(btnAddOne);
        modeltest = new DefaultComboBoxModel();
        comboBox = new JComboBox();
        comboBox.setBounds(48, 47, 129, 20);
        comboBox.setModel(modeltest);
        contentPane.add(comboBox);

        btnOpenSecondUi = new JButton("Open second UI");
        btnOpenSecondUi.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
               secondui= new SecondUI(OneUI.this); // pass reference of this oneui  to secondui .so secondui can catch reference of this class[this frame] and update this combobox by calling updateModelCmb on this reference

            }
        });
        btnOpenSecondUi.setBounds(155, 163, 161, 23);
        contentPane.add(btnOpenSecondUi);
    }

    public void updateModelCmb() {
        count++;
        modeltest.addElement(count);
        comboBox.setModel(modeltest);

    }

}
 
 SecondUI.java 
 
public class SecondUI extends JDialog {

    private final JPanel contentPanel = new JPanel();

    public SecondUI(OneUI oneui) {
        //setVisible(true); // don't call setvisible here call setvisible after you add all the component .
        setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
        setBounds(100, 100, 327, 142);
        getContentPane().setLayout(new BorderLayout());
        contentPanel.setLayout(new FlowLayout());
        contentPanel.setBorder(new EmptyBorder(5, 5, 5, 5));

        getContentPane().add(contentPanel, BorderLayout.CENTER);
        {
            JButton btnAddOneElement = new JButton("Add 1 element");
            btnAddOneElement.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    oneui.updateModelCmb();
                }
            });
            contentPanel.add(btnAddOneElement);
        }
        setVisible(true); // call setvisible at last
    }

}

in your SecondUI you are creating new instance of OneUI
 
final OneUI obj = new OneUI();
obj.setVisible(true);// you don't call even this
 
but you don't call it's visible to true.so there is a hidden jframe and combobox that combobox get updated but not first frame's combobox and you can't see updated combobox because the frame is not visible
 
to fix this pass oneui reference to secondui then call method of that reference 
 
example OneUI.java
 
public class OneUI extends JFrame {

    private JPanel contentPane;
    private JComboBox comboBox;
    private DefaultComboBoxModel modeltest;
    private Integer count = 0;
    private JButton btnOpenSecondUi;
    private SecondUI secondui;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            public void run() {
                OneUI frame = new OneUI();
                frame.setVisible(true);
            }
        });
    }

    public OneUI() {

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        JButton btnAddOne = new JButton("Add 1 element");
        btnAddOne.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                updateModelCmb();
            }
        });
        btnAddOne.setBounds(187, 46, 129, 23);
        contentPane.add(btnAddOne);
        modeltest = new DefaultComboBoxModel();
        comboBox = new JComboBox();
        comboBox.setBounds(48, 47, 129, 20);
        comboBox.setModel(modeltest);
        contentPane.add(comboBox);

        btnOpenSecondUi = new JButton("Open second UI");
        btnOpenSecondUi.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
               secondui= new SecondUI(OneUI.this); // pass reference of this oneui  to secondui .so secondui can catch reference of this class[this frame] and update this combobox by calling updateModelCmb on this reference

            }
        });
        btnOpenSecondUi.setBounds(155, 163, 161, 23);
        contentPane.add(btnOpenSecondUi);
    }

    public void updateModelCmb() {
        count++;
        modeltest.addElement(count);
        comboBox.setModel(modeltest);

    }

}
 
SecondUI.java
 
public class SecondUI extends JDialog {

    private final JPanel contentPanel = new JPanel();

    public SecondUI(OneUI oneui) {
        //setVisible(true); // don't call setvisible here call setvisible after you add all the component .
        setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
        setBounds(100, 100, 327, 142);
        getContentPane().setLayout(new BorderLayout());
        contentPanel.setLayout(new FlowLayout());
        contentPanel.setBorder(new EmptyBorder(5, 5, 5, 5));

        getContentPane().add(contentPanel, BorderLayout.CENTER);
        {
            JButton btnAddOneElement = new JButton("Add 1 element");
            btnAddOneElement.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    oneui.updateModelCmb();
                }
            });
            contentPanel.add(btnAddOneElement);
        }
        setVisible(true); // call setvisible at last
    }

}