How to load this ArrayList into a JTable

Question

I have a List (List<MyBean>). Then I used it for fill a 2D array. I used following steps to do it.

MyBean.java

public class MyBean{
private int id;
private String name;
private String address;

/**
 * @return the id
 */
public int getId()
{
    return id;
}

/**
 * @param id the id to set
 */
public void setId(int id)
{
    this.id = id;
}

/**
 * @return the name
 */
public String getName()
{
    return name;
}

/**
 * @param name the name to set
 */
public void setName(String name)
{
    this.name = name;
}

/**
 * @return the address
 */
public String getAddress()
{
    return address;
}

/**
 * @param address the address to set
 */
public void setAddress(String address)
{
    this.address = address;
}
}    

---

public void myMethod(List<MyBean> list){
    List<Object> objects = new ArrayList<>();
    for (Object object : list){
          objects.add(object != null ? object : null);
    }

    Object rowData1[][] = new Object[objects.size()][];
    for (int i = 0; i < objects.size(); i++){
          List<Object> row = (ArrayList<Object>)(Object)objects.get(i);
          rowData1[i] = row.toArray(new Object[row.size()]);
    }

    Object columnNames1[] ={"HEADER 1", "HEADER 2", "HEADER 3"};
} 

When I run execute this code I got following exception .

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException:
MyBean cannot be cast to java.util.ArrayList

The exception is on this line

List<Object> row = (ArrayList<Object>)(Object)objects.get(i);

I use this 2D array for following purpose.

JTable table1 = new TableWithRowHeader(rowData1, columnNames1);
table1.getColumnModel().getColumn(0).setPreferredWidth(120);

JScrollPane scrollPane1 = new JScrollPane(table1);
scrollPane1.setColumnHeaderView(null);

JPanel jPanel = new JPanel();
jPanel.setLayout(new BorderLayout());
JButton button = new JButton("Add Button");
button.addActionListener(new ActionListener(){

@Override
public void actionPerformed(ActionEvent ae){
      JDialog dialog = new JDialog();
      dialog.setTitle("terance");
      dialog.setSize(600, 500);
      dialog.setLocationRelativeTo(null);
      dialog.setVisible(true);
}
});

jPanel.removeAll();
jPanel.add(button, BorderLayout.EAST);
jPanel.revalidate();

JFrame frame = new JFrame("Testing");
frame.setLayout(new BorderLayout());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(jPanel, BorderLayout.NORTH);
frame.add(scrollPane1);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);

Here is an example sketch for final result .

How could I handle the exception ?

Have any ideas ?

Thank you .

Answer 1

Since you still have not told what you want the 2D array to look like, this is what I interpreted what you wanted.

Here I load a List<MyBean> of sample data

java.util.List<MyBean> list = new ArrayList<MyBean>();
for (int i = 0; i < 3; i++) {
    MyBean b = new MyBean();
    b.setId(i);
    b.setName("Name " + i);
    b.setAddress("Address " + i);
    list.add(b);
}

---

Here I load the Object[][] with that List<MyBean>. No casting required.

Object[][] data = new Object[list.size()][];
for (int i = 0; i < list.size(); i++) {
    MyBean b = list.get(i);
    Object[] row = new Object[] { b.getId(), b.getName(), b.getAddress() };
    data[i] = row;
}

Object columnNames1[] = {"HEADER 1", "HEADER 2", "HEADER 3"};

JTable table1 = new TableWithRowHeader(data, columnNames1);

Answer 2

• In your myMethod you are clearly passing a list of MyBean objects.

• From this list you are copying every MyBean instance to a new List called objects

• Then you are looping through objects and doing this: List<Object> row = (ArrayList<Object>)(Object)objects.get(i);

• But (Object)objects.get(i); here in this code will always return an Object of MyBean and not a list . This you can't typecast to an ArrayList. And thus the error!

You need to modify the code around rowData1 and objects list as per your requirement.