JTable shows a white box in the panel for unknown reasons

Question

I am building a swing application for a course. After I add my JTable to the panel, the table grids and column headers are not showing. Instead a white box appears in the panel where the table was supposed to be. Why is this happening and how to fix it ?

public class ReminderGui implements ActionListener {
JFrame frame;
JPanel panel;
JLabel lblTitle,lblDetails,lblDate,lblTime;
JTextField titleField,dateField;
JTextArea detailsArea;
JButton addButton,cancelButton,rmvButton,rmvallButton,editButton;
JTable table;
JComboBox<String> hourcbo,minutecbo,ampmcbo;
ArrayList<Reminder> remList;


final String hour[]={"12","1","2","3","4","5","6","7","8","9","10","11"};
final String minute[]={"00","01","02","03","04","05","06","07","08","09","10","11","12","13","14","15","16","17","18","19","20",
                     "21","22","23","24","25","26","27","28","29","30","31","32","33","34","35","36","37","38","39","40",
                     "41","42","43","44","45","46","47","48","49","50","51","52","53","54","55","56","57","58","59"
                    };
final String ampm[]={"AM","PM"};
String[] columnname={"Reminder Name", "Reminder Detail","Reminder Date","Reminder Time"};


public ReminderGui() throws FileNotFoundException, IOException, ClassNotFoundException{

    panel=new JPanel();
    panel.setLayout(null);

    lblTitle=new JLabel("Reminder Title");
    lblDetails=new JLabel("Reminder Details");
    lblDate=new JLabel("Set Date(date/motnth/year)");
    lblTime=new JLabel("Set Time");

    titleField=new JTextField();
    titleField.setMargin(new Insets(5,5,5,5));


    detailsArea=new JTextArea(10,20);
    detailsArea.setLineWrap(true);
    detailsArea.setMargin(new Insets(5,5,5,5));
    JScrollPane scroller1=new JScrollPane(detailsArea);
    scroller1.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
    scroller1.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);


    //date and time component     

    dateField=new JTextField();
    dateField.setMargin(new Insets(5,5,5,5));


    hourcbo=new JComboBox<String>(hour);
    hourcbo.setBackground(Color.white);
    minutecbo=new JComboBox<String>(minute);
    minutecbo.setBackground(Color.white);
    ampmcbo=new JComboBox<String>(ampm);
    ampmcbo.setBackground(Color.white);

    addButton=new JButton("Add");
    cancelButton=new JButton("Cancel");
    editButton=new JButton("Edit");
    rmvButton=new JButton("Remove Selected");
    rmvallButton=new JButton("Remove all");  



    lblTitle.setBounds(30, 30, 100, 30);
    panel.add(lblTitle);
    titleField.setBounds(150, 30, 400, 30);
    panel.add(titleField);
    lblDetails.setBounds(30, 80, 100, 30);
    panel.add(lblDetails);
    scroller1.setBounds(150, 80, 400, 200);
    panel.add(scroller1);
    lblDate.setBounds(30, 310, 170, 30);
    panel.add(lblDate);
    dateField.setBounds(210, 310, 100, 30);
    panel.add(dateField);
    lblTime.setBounds(340, 310, 50, 30);
    panel.add(lblTime);
    hourcbo.setBounds(400, 310, 100, 30);
    minutecbo.setBounds(510, 310, 100, 30);
    ampmcbo.setBounds(620, 310, 100, 30);
    panel.add(hourcbo);
    panel.add(minutecbo);
    panel.add(ampmcbo);
    addButton.setBounds(30,380,100,30);
    panel.add(addButton);
    cancelButton.setBounds(160,380,100,30);
    panel.add(cancelButton);



    File file=new File("appFile.chk");
    Object[][] data = null;
    if(!(file.exists())){
        remList=new ArrayList<Reminder>();
        ObjectOutputStream oos=new ObjectOutputStream(new FileOutputStream(file));
        oos.writeObject(remList);
    oos.flush();
    oos.close();
    }

        ObjectInputStream ois=new ObjectInputStream(new FileInputStream(file));
        remList=(ArrayList<Reminder>)ois.readObject();
        int rownum=remList.size();
        data=new String[rownum][4];
        Iterator<Reminder> it=remList.iterator();
        Reminder rem=null;
        for(int i=0;i<rownum;i++){
            if(it.hasNext()){
                rem=it.next();
            }

            data[i][0]=rem.getReminderTitle();
            data[i][1]=rem.getReminderDetails();
            data[i][2]=rem.getReminderDate();
            data[i][3]=rem.getReminderTime();
        }

        ois.close();



    //jtable

    table=new JTable(data,columnname);
    table.setBounds(160,450,400,300);


    JScrollPane scroller2=new JScrollPane(table);
    scroller1.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
    scroller1.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
    panel.add(table);


    addButton.addActionListener(this);
    cancelButton.addActionListener(this);
    editButton.addActionListener(this);
    rmvButton.addActionListener(this);
    rmvallButton.addActionListener(this);



    //set framesize when other works are done
    frame=new JFrame("RemindMe!");
    frame.add(panel);
    frame.setSize(850,840); 
    frame.setVisible(true);
    frame.setLocationRelativeTo(null);
    frame.setResizable(false);
}

@Override
public void actionPerformed(ActionEvent e) {
    //throw new UnsupportedOperationException("Not supported yet.");
    if(e.getSource()==addButton){
        String s1=(String)titleField.getText();
        String s2=(String)detailsArea.getText();
        String s3=(String)dateField.getText();
        String s4=(String)hourcbo.getSelectedItem()+":"+(String)minutecbo.getSelectedItem()+" "+(String)ampmcbo.getSelectedItem();

    }
    else if(e.getSource()==cancelButton){
        titleField.setText("");
        detailsArea.setText("");
        dateField.setText("");

    }



}

Answer 1

You've added the JTable to more than one container -- both the JScrollPane's viewport (good) and also to the panel JPanel (bad). This second action removes the JTable from the JScrollPane, so that later when you add the JScrollPane to panel, it holds nothing.

JScrollPane scroller2=new JScrollPane(table);

Good!

panel.add(table);

Bad!

Solution: don't do that. Add your components to one and only one container.

Other problems:

panel.setLayout(null);

Don't use null layouts, as these lead to fragile GUI's that look sort-of OK on one platform and not so good on others, and that are very difficult to debug and enhance. Learn and use the layout managers.