无法解决SQLException: ColumnIndex超出范围

Question

java.sql.SQLException: Column index out of range.
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1094)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:997)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:983)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:928)
    at com.mysql.jdbc.ResultSetMetaData.getField(ResultSetMetaData.java:407)
    at com.mysql.jdbc.ResultSetMetaData.getColumnName(ResultSetMetaData.java:258)
    at a.MyFrame.createTablePanel(MyFrame.java:58)
    at a.MyFrame.<init>(MyFrame.java:24)
    at a.MyFrame.main(MyFrame.java:19)

这是我在MyFrame类中得到的堆栈跟踪。这些是代码:

MyFrame.createTablePanel().
public JPanel createTablePanel () {
        DefaultTableModel tableModel = new DefaultTableModel();
        DB dB = new DB();
        dB.connectDB();
        ResultSet rs = dB.getData();
        try {       
            ResultSetMetaData rsMD = rs.getMetaData();
            String[] arr = new String[rsMD.getColumnCount()];
            for (int i = 0; i <= rsMD.getColumnCount(); i++) {
                arr[i] = rsMD.getColumnName(i+1);
            }
            tableModel.setColumnIdentifiers(arr);
            while (rs.next()) {
                for (int i = 0; i <= rsMD.getColumnCount(); i++) {
                    arr[i] = rs.getString(i+1);
                }
                tableModel.addRow(arr);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        JPanel tablePanel = new JPanel(new BorderLayout(5,5));
        JTable table = new JTable(tableModel);
        tablePanel.add(new JScrollPane(table), BorderLayout.CENTER);
        return tablePanel;
    }

它使用DB类与数据库通信:

DB Class.
public class DB {
    private final String driver = "com.mysql.jdbc.Driver";
    private final String url = "jdbc:mysql://localhost:3306/test";
    private final String user = "root";
    private final String pass = "khjthat";
    private final String table = "ungvien";
    Statement stmt;
    PreparedStatement pstmt;
    ResultSet rs;
    ResultSetMetaData rsMD;
    String str; //Query String.
    Connection connection;
    public DB() {
    }
    public void connectDB () {
        try {
            Class.forName(driver);
                System.out.println("Driver Loaded!");
            connection = DriverManager.getConnection(url,user,pass);
                System.out.println("Connected!");
        } catch (ClassNotFoundException e) {
            System.out.println("Class Not Found!");
        } catch (SQLException e) {
            System.out.println("Connection Error!");
        }
    }
    public void showData(ResultSet rs) {
            try {
                rsMD = rs.getMetaData();
                for (int i = 0; i < rsMD.getColumnCount(); i++) {
                    System.out.printf("t%-10s ", rsMD.getColumnName(i+1));
                }
                System.out.println();
                while (rs.next()) {
                    System.out.printf("t%-10s t%-10s t%-10s t%-10s n", rs.getString(1), rs.getString(2), rs.getString(3), rs.getString(4));
                }
            } catch (SQLException e) {
            }
    }
    public ResultSet getData() {
        str = "select * from " + table + ";";
        try {
            stmt = connection.createStatement();
            rs = stmt.executeQuery(str);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return rs;
    }
    public ResultSet getDataTen(String ten) {
        str = "select ten,tuoi,truong,kn from " + table + " where ten = ? " ;
        try {
            pstmt = connection.prepareStatement(str);
            pstmt.setString(1, ten);
            rs = pstmt.executeQuery();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return rs;
    }
    public void deleteTen (String ten) {
        str = "delete from " + table + " where ten = ? ";
        try {
            pstmt = connection.prepareStatement(str);
            pstmt.setString(1, ten);
            if (pstmt.executeUpdate() > 0) {
                System.out.println("Delete Successful!");
            } else {
                System.out.println("Delete Error!");
            }
        } catch (SQLException e) {
            System.out.println("Delete Error!");
            e.printStackTrace();
        }
    }
    public void insert (UngVien ungVien) {
        str = "insert into " + table + " values (?,?,?,?) ";
        try {
            pstmt = connection.prepareStatement(str);
            pstmt.setString(1, ungVien.getTen());
            pstmt.setInt(2, ungVien.getTuoi());
            pstmt.setString(3, ungVien.getTruong());
            pstmt.setInt(4, ungVien.getKn());
            if (pstmt.executeUpdate() > 0) {
                System.out.println("Insert Successful!");
            } else {
                System.out.println("Insert Error!");
            }
        } catch (SQLException e) {
            System.out.println("Insert Error!");
            e.printStackTrace();
        }
    }
    public void updateTen (String ten, UngVien ungVien) {
        str = "update " + table + " set tuoi =?, truong =?, kn =? where ten = ?";
        try {
            pstmt = connection.prepareStatement(str);
            pstmt.setInt(1, ungVien.getTuoi());
            pstmt.setString(2, ungVien.getTruong());
            pstmt.setInt(3, ungVien.getKn());
            pstmt.setString(4, ten);
            if (pstmt.executeUpdate() > 0) {
                System.out.println("Update Successful!");
            } else {
                System.out.println("Update Error!");
            }
        } catch (SQLException e) {
            System.out.println("Update Error!");
            e.printStackTrace();
        }
    }
    public static void main (String[] args) {
        DB dB = new DB();
        dB.connectDB();
        dB.showData(dB.getData());
    }
}

我测试了DB类，一切正常。

我试着调试这个整个下午，但我不能理解如果它就在那里:(

我是JAVA的新手，我希望这个问题没有打扰到你们。

请给我一些技巧。

Answer 1

正如user3145373在评论中提到的

从

for (int i = 0; i <= rsMD.getColumnCount(); i++)

删除equal(=)号，按

for (int i = 0; i < rsMD.getColumnCount(); i++)

Answer 2

进一步解释上述答案

假设有人让你给我10个硬币，并将第一枚硬币的计数设为0，那么在这种情况下，你会一直给他，直到数到9为止。

同样的情况，你已经初始化了i = 0，所以你需要迭代它，直到计数达到totalCount-1。

或者改成

for (int i = 1; i <= rsMD.getColumnCount(); i++)