String sName = new String()

This line of code creates a new instance of the String class and assigns it to the variable sName. However, since no value is provided as an argument to the String constructor, the string will be empty.

相关问题

private void button3_Click_1(object sender, EventArgs e) { string sno = "20006666"; string sname = "行子"; string ssex = "男"; int sage = 22; string sdept = "ma"; try { string str = "server=localhost;User Id=root;password=123456;Database=class"; MySqlConnection conn = new MySqlConnection(str); string sql = $"insert into student (sno,sname, ssex,sage,sdept) values (sno,sname,ssex,sage,sdept)"; MySqlCommand cmd = new MySqlCommand(sql, conn); conn.Open(); int result = cmd.ExecuteNonQuery(); conn.Close(); if (result > 0) { MessageBox.Show("数据插入成功"); } else { MessageBox.Show("数据插入失败"); } } catch (Exception ex) { MessageBox.Show(ex.Message); } }

这段代码是一个插入操作，将学生信息插入到数据库中。具体来说，它连接到名为"class"的数据库，在其中的"student"表中插入一行数据，该行数据由变量"sno"、"sname"、"ssex"、"sage"和"sdept"组成。

值得注意的是，这段代码有可能会出现异常，比如数据库连接失败、SQL语句执行失败等等，因此在try-catch语句块中对异常进行了处理。如果执行成功，会弹出一个提示框表示插入数据成功；否则会提示插入失败。

修改这段代码实现选择表格一行信息删除package frame; import javax.swing.; import java.awt.; import java.awt.event.ActionEvent; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.SQLException; //添加页面 public class EditDialog extends BaseDialog{ DataChangelisenter dataChangelisenter; public void setDataChangelisenter(DataChangelisenter dataChangelisenter) { this.dataChangelisenter = dataChangelisenter; } @Override public void init() { setLayout(new FlowLayout()); //布局 setTitle("修改图书信息"); JPanel jp0=new JPanel(); JLabel l0 = new JLabel("id"); JTextField t0 = new JTextField(); t0.setPreferredSize(new Dimension(300,30)); jp0.add(l0); jp0.add(t0); JPanel jp1=new JPanel(); JLabel l1 = new JLabel("书名"); JTextField t1 = new JTextField(); t1.setPreferredSize(new Dimension(300,30)); jp1.add(l1); jp1.add(t1); JPanel jp2=new JPanel(); JLabel l2 = new JLabel("作者"); JTextField t2 = new JTextField(); t2.setPreferredSize(new Dimension(300,30)); jp2.add(l2); jp2.add(t2); JPanel jp3=new JPanel(); JLabel l3 = new JLabel("分类"); JTextField t3 = new JTextField(); t3.setPreferredSize(new Dimension(300,30)); jp3.add(l3); jp3.add(t3); JPanel jp4=new JPanel(); JLabel l4 = new JLabel("出版社"); JTextField t4 = new JTextField(); t4.setPreferredSize(new Dimension(300,30)); jp4.add(l4); jp4.add(t4); JPanel jp5=new JPanel(); JLabel l5 = new JLabel("数量"); JTextField t5 = new JTextField(); t5.setPreferredSize(new Dimension(300,30)); jp5.add(l5); jp5.add(t5); add(jp0); add(jp1); add(jp2); add(jp3); add(jp4); add(jp5); JButton b1 = new JButton("保存"); b1.setPreferredSize(new Dimension(150,30)); b1.addActionListener(new AbstractAction() { @Override public void actionPerformed(ActionEvent e) { String id = t0.getText(); String sname = t1.getText(); String author = t2.getText(); String classify = t3.getText(); String press = t4.getText(); String quantity = t5.getText(); Connection con = DBUtil.getConnect(); String sql = "UPDATE tushu SET sname=?,author=?,classify=?,press=?,quantity=? WHERE id=?"; try { PreparedStatement ps = con.prepareStatement(sql); ps.setString(1,sname); ps.setString(2,author); ps.setString(3,classify); ps.setString(4,press); ps.setString(5,quantity); ps.setString(6,id); int result = ps.executeUpdate(); if (result>0){ JOptionPane.showMessageDialog(EditDialog.this,"修改成功"); // new StudentFrame(); dataChangelisenter.dataChange(); dispose(); }else { JOptionPane.showMessageDialog(EditDialog.this,"修改失败"); } } catch (SQLException throwables) { throwables.printStackTrace(); } } }); add(b1); } }

修改后的代码如下：

package frame;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class EditDialog extends BaseDialog{
    DataChangelisenter dataChangelisenter;
    JTable table;

    public void setDataChangelisenter(DataChangelisenter dataChangelisenter) {
        this.dataChangelisenter = dataChangelisenter;
    }

    public void setTable(JTable table) {
        this.table = table;
    }

    @Override
    public void init() {
        setLayout(new FlowLayout());  // 布局
        setTitle("修改图书信息");

        JPanel jp0 = new JPanel();
        JLabel l0 = new JLabel("id");
        JTextField t0 = new JTextField();
        t0.setPreferredSize(new Dimension(300, 30));
        jp0.add(l0);
        jp0.add(t0);

        JPanel jp1 = new JPanel();
        JLabel l1 = new JLabel("书名");
        JTextField t1 = new JTextField();
        t1.setPreferredSize(new Dimension(300, 30));
        jp1.add(l1);
        jp1.add(t1);

        JPanel jp2 = new JPanel();
        JLabel l2 = new JLabel("作者");
        JTextField t2 = new JTextField();
        t2.setPreferredSize(new Dimension(300, 30));
        jp2.add(l2);
        jp2.add(t2);

        JPanel jp3 = new JPanel();
        JLabel l3 = new JLabel("分类");
        JTextField t3 = new JTextField();
        t3.setPreferredSize(new Dimension(300, 30));
        jp3.add(l3);
        jp3.add(t3);

        JPanel jp4 = new JPanel();
        JLabel l4 = new JLabel("出版社");
        JTextField t4 = new JTextField();
        t4.setPreferredSize(new Dimension(300, 30));
        jp4.add(l4);
        jp4.add(t4);

        JPanel jp5 = new JPanel();
        JLabel l5 = new JLabel("数量");
        JTextField t5 = new JTextField();
        t5.setPreferredSize(new Dimension(300, 30));
        jp5.add(l5);
        jp5.add(t5);

        add(jp0);
        add(jp1);
        add(jp2);
        add(jp3);
        add(jp4);
        add(jp5);

        JButton b1 = new JButton("保存");
        b1.setPreferredSize(new Dimension(150, 30));
        b1.addActionListener(new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String id = t0.getText();
                String sname = t1.getText();
                String author = t2.getText();
                String classify = t3.getText();
                String press = t4.getText();
                String quantity = t5.getText();
                Connection con = DBUtil.getConnect();
                String sql = "UPDATE tushu SET sname=?,author=?,classify=?,press=?,quantity=? WHERE id=?";
                try {
                    PreparedStatement ps = con.prepareStatement(sql);
                    ps.setString(1,sname);
                    ps.setString(2,author);
                    ps.setString(3,classify);
                    ps.setString(4,press);
                    ps.setString(5,quantity);
                    ps.setString(6,id);
                    int result = ps.executeUpdate();
                    if (result > 0){
                        JOptionPane.showMessageDialog(EditDialog.this,"修改成功");
                        // 删除选中的行
                        int selectedRow = table.getSelectedRow();
                        DefaultTableModel model = (DefaultTableModel) table.getModel();
                        if (selectedRow != -1) {
                            model.removeRow(selectedRow);
                        }
                        dataChangelisenter.dataChange();
                        dispose();
                    }else {
                        JOptionPane.showMessageDialog(EditDialog.this,"修改失败");
                    }
                } catch (SQLException throwables) {
                    throwables.printStackTrace();
                }
            }
        });

        add(b1);
    }
}

在这个代码中，我们添加了一个 `setTable` 方法，用于设置需要操作的表格对象。然后，在保存按钮的事件监听器中，我们通过 `table.getSelectedRow()` 来获取当前选中的行，然后使用 `DefaultTableModel` 的 `removeRow` 方法来删除该行数据。最后，我们调用 `dataChangelisenter.dataChange()` 方法来通知主界面数据已经发生了改变。