当我点击运行按钮时，我的 JFrame 不会出现，尽管 NetBeans 说它正在运行

Question

I created a simple form by NetBeans. Everythings worked fine but when I add some codes for the JTabel, it won't show up anything when I hit run. This is my code:

public final class QuanLy extends javax.swing.JFrame {
    public QuanLy() {
        initComponents();
        show();
    }

    public ArrayList<Subject> subjectList(){
        ArrayList<Subject> subjectsList = new ArrayList<>();
        try {
            Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
            String url = "jdbc:sqlserver://localhost;databaseName=QLLTCK;integratedSecurity=true;";
            Connection connection = DriverManager.getConnection(url);
            Statement statement = connection.createStatement();
            ResultSet resultSet = statement.executeQuery("SELECT * FROM PHANCONG");

            while(resultSet.next()){
                Subject subject = new Subject(resultSet.getString("maLop"), resultSet.getString("tenMH"), 
                        resultSet.getString("ngayThi"), resultSet.getInt("caThi"), resultSet.getString("phongThi"), 
                        resultSet.getInt("soSV"), resultSet.getInt("soCBCT"), resultSet.getString("xepLoai"));
                subjectsList.add(subject);
            }
        }
        catch(Exception sqlex){
            sqlex.printStackTrace();
        }        
        return subjectsList;
    }

    @Override
    public void show(){
        ArrayList<Subject> list = subjectList();
        DefaultTableModel model = (DefaultTableModel)table.getModel();
        Object[] row = new Object[8];
        for(int i = 0; i < list.size(); i++){
            row[0] = list.get(i).getMaLop();
            row[1] = list.get(i).getTenMH();
            row[2] = list.get(i).getNgayThi();
            row[3] = list.get(i).getCaThi();
            row[4] = list.get(i).getPhongThi();
            row[5] = list.get(i).getSoSV();
            row[6] = list.get(i).getSoCBCT();
            row[7] = list.get(i).getXepLoai();
            model.addRow(row);
        }
    }
//... (those lines are created by NetBeans)
}

When I comment out the show(), public ArrayList subjectList() and public void show(), my form show up normally.

This is the image. Running but not showing. https://imgur.com/ibAH1ML

This is the project without the codes I have shown. https://imgur.com/Ha04mwl

Can someone help me? Thanks.

Sorry for my bad English.

Answer 1

You are overriding the show function but you are not implementing a display logic or calling the super show. The easiest would be to just call super.show() at the end of your show function

Answer 2

First of all the show() method is deprecated. You should use setVisible(true) instead.

Secondly, it is not good practice to do an overridable method call in constructor, since this could lead to undesired bugs. Constructors should never invoke overridable methods, directly or indirectly, because the superclass constructor runs before the subclass constructor, so the overriding method in the subclass will be invoked before the subclass constructor has run. If the overriding method depends on any initialization performed by the subclass constructor, the method will not behave as expected.

What you can do, is to rename your show() method to initTable() for instance, and call it just after your form has been created. If you created in the main method for instance, you could do something like:

public static void main(String[] args) {
     QuanLy frame = new QuanLy();

     // ... other initialization stuff ...

     frame.setVisible(true);
     frame.initTable(); // the initTable is you show() method renamed

     // ... rest of your code ...

}

Answer 3

The recommended way of doing this is like this

SwingUtilities.invokeLater(() -> {
    frame.pack();
    frame.setVisible(true);
});

The lambda can also be replaced with a Runnable object with its run method being overridden.

Don't use the .show() method as it has been deprecated.