Class Cast exception on DefaultTableModel

Question

I have 3 Class

firs for get data from database

second for common works

other for show table.

public class TableContent {

private final Vector<String> headers;
private final Vector<Vector<String>> content;

public TableContent(final Vector<String> headers, final Vector<Vector<String>> content) {
    this.headers = headers;
    this.content = content;
}

public Vector<String> headers() {
    return headers;
}

public Vector<Vector<String>> content() {
    return content;
}
}

And:

public class TableData {

public TableContent getData() {
    Vector<String> headers = new Vector<String>();
    Vector<Vector<String>> content = new Vector<Vector<String>>();

    try {
        Connection conn = DriverManager.getConnection("");
        Statement statement = conn.createStatement();
        ResultSet rs = statement.executeQuery("Select * from table");

        headers = buildHeaders(rs);
        content = buildContent(rs);

    } catch (SQLException e) {
        e.printStackTrace();
    }

    return new TableContent(headers, content);
}

private Vector<String> buildHeaders(final ResultSet rs) throws SQLException {
    Vector<String> headers = new Vector<String>();

    int col = rs.getMetaData().getColumnCount();
    for (int i = 1; i <= col; i++) {
        headers.add(rs.getMetaData().getColumnName(i));
    }
    return headers;
}

private Vector<Vector<String>> buildContent(final ResultSet rs) throws SQLException {
    Vector<Vector<String>> content = new Vector<Vector<String>>();

    while (rs.next()) {
        int col = rs.getMetaData().getColumnCount();
        Vector<String> newRow = new Vector<String>(col);

        for (int i = 1; i <= col; i++) {
            newRow.add(rs.getString(i));
        }
        content.add(newRow);
    }
    return content;
}
}

And:

public class TableGUI extends JFrame {

JTable table;
TableContent data = new TableData().getData();

public TableGUI() {
    table = new JTable(new DefaultTableModel(data.headers(), data.content()));

    add(new JScrollPane(table), BorderLayout.CENTER);

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(700, 550);
    setLocation(300, 80);
    setVisible(true);
}

public static void main(String[] args) {
    new TableGUI();
}
}

Output:

Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.util.Vector
at javax.swing.table.DefaultTableModel.justifyRows(DefaultTableModel.java:268)
at javax.swing.table.DefaultTableModel.setDataVector(DefaultTableModel.java:224)
at javax.swing.table.DefaultTableModel.<init>(DefaultTableModel.java:159)
at TableGUI.<init>(TableGUI.java:11)
at TableGUI.main(TableGUI.java:22)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

where is my mistake?

Answer 1

I strongly suspect the problem is that you're passing the arguments in the wrong order. The first parameter of DefaultTableModel(Vector, Vector) is meant to be the data. It's the second parameter which is meant to be the column names. So try this:

table = new JTable(new DefaultTableModel(data.content(), data.headers()));

Answer 2

I thing you are passing the wrong arguments to the constructor. According to the constructor documentation you have to pass the content as first and the header data as second parameter.

So you should try flipping the parameters of DefaultTableModel in your code:

table = new JTable(new DefaultTableModel(data.content(), data.headers()));