Question

我正在尝试使用java swing中的表创建一个表并向sql添加值。但是在for循环中我根本没有递增。我认为它是因为while(rs2.next())。当我把它放在for循环中时，我得到这个错误：“在开始结果集之前”。我需要帮助！

编辑：处理上述问题但我现在遇到了新问题。似乎JTable没有更新自己。当我在组合框表中选择一个表名时应用程序崩溃并给出数组索引超出范围的异常。

我的代码在这里：

public class DBC extends JFrame{

static String tablo;
static JTextField tf = new JTextField(20);
static int columnCount;
static JPanel tfPanel = new JPanel();
static String[] sutunlar;
static JLabel sutunLabel;
static JPanel sutunPanel = new JPanel(new BorderLayout());
static JTable table;
static JScrollPane scrollPane;

public static void main(String[] args) throws Exception {

    Class.forName("com.mysql.jdbc.Driver");
    Connection connect = DriverManager.getConnection("jdbc:mysql://localhost:3306/project"
              ,"root","123456789");

    final Statement statement = connect.createStatement();

    JLabel tabloSec = new JLabel("Tablo Seçin:");
    final JComboBox<String> tablolar = new JComboBox<String>();
    final DatabaseMetaData md = connect.getMetaData();
    final ResultSet rs = md.getTables(null, null, "%", null);

    while (rs.next()) {
        tablolar.addItem(rs.getString(3));
    }

    tablolar.addActionListener(new ActionListener(){

        @Override
        public void actionPerformed(ActionEvent arg0) {

            tablo = tablolar.getSelectedItem().toString();

            try {

                 ResultSet rs2 = statement.executeQuery("SELECT * FROM "+tablo);
                 ResultSetMetaData rsmd = rs2.getMetaData();
                 columnCount = rsmd.getColumnCount();

                 sutunlar = new String[columnCount];
                 table = new JTable(1,columnCount);
                 Object columnNames[] = new Object[columnCount];
                 Object rowData[][] = {{""}};

                     for(int i=0;i<columnCount;i++){

                         sutunlar[i] = rsmd.getColumnLabel(i+1);
                         columnNames[i] = sutunlar[i];

                         }

                     table = new JTable(rowData, columnNames);
                     table.repaint();
                     scrollPane = new JScrollPane(table);
                     sutunPanel.add(scrollPane);
                     sutunPanel.revalidate();

            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    });

    JButton ekle = new JButton("Ekle");
    ekle.addActionListener(new ActionListener(){

        @Override
        public void actionPerformed(ActionEvent e) {

            try {
                switch(tablo){
                case "department":

                    statement.executeUpdate("INSERT INTO department(Name,Location) VALUES('"+tf.getText()+"')");
                case "employee":

                    statement.executeUpdate("INSERT INTO employee(Id,FirstName,LastName,Sex,Address,Email,Salary,BirthDate,JoinDate) VALUES('"+tf.getText()+"')");
                case "engineer":

                    statement.executeUpdate("INSERT INTO engineer(EngineerType) VALUES('"+tf.getText()+"')");
                case "manager":

                    statement.executeUpdate("INSERT INTO manager(Department) VALUES('"+tf.getText()+"')");
                case "project":

                    statement.executeUpdate("INSERT INTO project(Name,Number,Value) VALUES('"+tf.getText()+"')");
                case "secretary":

                    statement.executeUpdate("INSERT INTO secretary(TypingSpeed) VALUES('"+tf.getText()+"')");
                }

            } catch (SQLException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
        }
    });

    JButton cik = new JButton("Çık");
    cik.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {

            System.exit(0);
        }
    });

    JPanel panel = new JPanel(new FlowLayout());

    panel.add(tabloSec);
    panel.add(tablolar);
    panel.add(sutunPanel);
    panel.revalidate();
    panel.add(ekle);
    panel.add(cik);

    JFrame frame = new JFrame("Deneme");
    frame.setSize(600,600);
    frame.setLocationRelativeTo(null);
    frame.add(panel);
    frame.setVisible(true);
  }
}

Answer 1

我认为for循环没有问题。

while(rs2.next()){

}

如果在i的其他迭代条件为false时执行此操作，则它不会在循环时进入。

如果你想测试你可以做：

for(int i=0;i<columnCount;i++){  

    while(rs2.next()){              

       sutunlar[i] = rs2.getString(4);
       Set<String> setSutunlar = new HashSet<>(Arrays.asList(sutunlar[i]));
       Object rowData[][] = {null};
       Object columnNames[] = setSutunlar;
       table = new JTable(rowData, columnNames);
       scrollPane = new JScrollPane(table);
       sutunPanel.add(scrollPane);
    }

    System.out.println("Value of i is " + i);// Add this line to check iteration of i.
}

Answer 2

我认为你混淆了一些东西。定义时

columnCount = rsmd.getColumnCount();

您似乎期望columnCount保存表的列数;但这种情况并非如此。这是元数据提供的列数。

如果要获取所选表格的列名称，请将其放在try/catch块中：

ResultSet rs2 = md.getColumns(null, null, tablo, null);

Set<String> columnNames = new HashSet<String>();
while (rs2.next()) {
  columnNames.add(rs2.getString(4));
}

Object[][] rowData = { null };
table = new JTable({ null }, columnNames.toArray());
scrollPane = new JScrollPane(table);
sutunPanel.add(scrollPane);

你应该考虑使用静态字段;）

JTable没有更新

2 个答案: