Question

The scrollbar and the button will be painted but not the cells in the table,and the console has printed the data correctly so I am wondering where I have done wrong.

public class MyGUIManager extends JPanel {

    protected JFrame frame;
    protected JScrollPane scrollPane=null;
    protected JTable table=null;
    protected TableModel model=null;
    protected JButton btnInsert=null;

    protected String dbname,tblname;
    protected Vector<String> colNames;
    protected Vector<Vector<String>> data,backup;
    protected int col;

    protected MySQLGUIManager() throws Exception{

        frame =new JFrame("MySQL Manager");
        frame.setContentPane(this);
        frame.setMinimumSize(new Dimension(800,600));
        frame.pack();
        frame.setVisible(true);
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());
        init();
    }

    protected void init() throws Exception{
        //some inrrelevant operations about database
        loadTbl();
    }

    protected void loadTbl() throws SQLException{
        table=new JTable(data,colNames){
            private static final long serialVersionUID = 1L;
            public void tableChanged(TableModelEvent e){
                int column=e.getColumn();
                assert e.getFirstRow()==e.getLastRow():"more than 1 row have been changed!";
                int row=e.getFirstRow();
                if(scrollPane!=null){
                    //some codes
                }
            }
        };

        model=table.getModel();
        scrollPane=new JScrollPane(table,JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        add(scrollPane,BorderLayout.CENTER);
        btnInsert=new JButton("Insert a row");
        add(btnInsert,BorderLayout.SOUTH);
        repaint();
        revalidate();
//      scrollPane.repaint();
//      scrollPane.revalidate();
        System.out.println(model.getColumnCount()+" "+model.getRowCount());
        for(int i=0;i<data.size();i++){
            for(int j=0;j<data.get(0).size();j++){
                System.out.print(model.getValueAt(i, j)+" ");
            }
            System.out.println();
        }
    }

    public static void main(String[] args) throws Exception {
        new MySQLGUIManager();
    }

}

(Some codes are omitted but they have nothing to do with GUI.)
Thanks in advance!

Answer 1

• Nothing is added to the data/column models
• The data and column models are uninitialized
• Creating a JFrame from within a JPanel only to add itself to the frame is bad practice

You’re not call super.tableChanged from within you tableChanged method

table = new JTable(data, colNames) {
    private static final long serialVersionUID = 1L;

    public void tableChanged(TableModelEvent e) {
        super.tableChanged(e);
        int column = e.getColumn();
        assert e.getFirstRow() == e.getLastRow() : "more than 1 row have been changed!";
        int row = e.getFirstRow();
        if (scrollPane != null) {
            //some codes
        }
    }
};