向JFrame中添加JTable

Question

我想将test2添加到我的DFrametest类中，以便test2的表显示在我的窗口中。我得到一个空窗口，找不到错误。

public class test2 extends JPanel {
    JTable tbl;
    DefaultTableModel dt;
    public test2(){
        JLabel label = new JLabel("Course Lookup GUI");
        this.add( label );
        tbl = new JTable();
        dt = new DefaultTableModel();
        dt.addColumn("ID");
        dt.addColumn("Name");
        tbl.setModel(dt);
        try{
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/lagerverwaltungwin", "root", "");
            Statement st = con.createStatement();
            ResultSet rs = st.executeQuery("SELECT ArtNr, Beschreibung FROM artikel");  
        }catch(Exception e){
            e.printStackTrace();
        }
        JScrollPane jp = new JScrollPane();
        jp.getViewport().add(tbl);
        add(jp);
    }
}

这是我的Frameclass，它应该有test2的表:

public class DFrametest extends JFrame {
    private JPanel contentPane;
    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    DFrametest frame = new DFrametest();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
    public DFrametest() {
        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);
        test2 t = new test2();
        this.add(t);
        this.setVisible(true);
    }
}

Answer 1

永远不要使用null布局。也不要使用setBounds(100, 100, 450, 300);使用pack();

像这样改变你的DFrametest类

        contentPane.setLayout(new BorderLayout());
        contentPane.add(t, BorderLayout.CENTER);

DFrametest类的完整代码:

public class DFrametest extends JFrame {
    private JPanel contentPane;
    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    DFrametest frame = new DFrametest();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
    public DFrametest() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        test2 t = new test2();
        contentPane.setLayout(new BorderLayout());
        contentPane.add(t, BorderLayout.CENTER);
        pack();
    }
}

Answer 2

尝试使用setBounds()方法，因为您没有提到任何布局(setLayout是null)。在将jpanel添加到jframe

之前添加setBounds方法

setBounds(x-axis,y-axis,width,height);

交货:

   setBounds(10,20,200,400);

注意: