java - java中的IF ELSE语句删除sql joption消息

Question

我尝试创建一个 if 语句，但不起作用，如果在 jtable 中找到 isbn book，则显示消息“book”删除”，否则找不到“book”。这可能吗？

 private void elimina_libroActionPerformed(java.awt.event.ActionEvent evt) {      
   Connection conn = Connessione.ConnecrDb();
   Statement stmt = null;
   ResultSet emps = null;       
      boolean found = false;
    try{          
      if(emps.next()) 
      found= true;
        String sql= "DELETE FROM progetto.libro WHERE isbn =?";  
        pst=(OraclePreparedStatement) conn.prepareStatement(sql);            
        pst.setString (1, txt_isbn.getText());          
        pst.execute();               

    if (!found)
       JOptionPane.showMessageDialog(null, "LIBRO ELIMINATO"); 
   else{    
            JOptionPane.showMessageDialog(null, "BOOK NOT FOUND","ERRORE",jOptionPane.WARNING_MESSAGE); 

    }

    }
    catch (Exception e)
     {
      JOptionPane.showMessageDialog(null,e);
                }    

但是不行，你能帮我吗？谢谢

我用这个更改代码

Connection conn = Connessione.ConnecrDb();
   Statement stmt = null;
   ResultSet emps = null;

    try{

        String sql= "DELETE FROM progetto.libro WHERE isbn =?"; 

        pst=(OraclePreparedStatement) (PreparedStatement) conn.prepareStatement(sql);            
          pst.setString (1, txt_isbn.getText());          
        int deleted = pst.executeUpdate();               

if (deleted == 0) {

         JOptionPane.showMessageDialog(null, "LIBRO ELIMINATO");
         Update_table(); 


          }else
               JOptionPane.showMessageDialog(null, "LIBRO NON TROVATO");  

    }

    catch (Exception e)
     {
      JOptionPane.showMessageDialog(null,e);

    }    

但是，如果我插入不正确的 isbn，则消息为:“图书删除”，如果我插入正确的 isbn，则消息为“未找到图书”，如果我再次插入正确的 isbn，则消息为“图书删除”，并且图书从数据库中删除。

Answer 1

    pst=(PreparedStatement) conn.prepareStatement(sql);            
    pst.setString (1, txt_isbn.getText());          
    int deleted = pst.executeUpdate();               

    if (deleted == 0) {
    ...

int executeUpdate() throws SQLException

Executes the SQL statement in this PreparedStatement object, which must be an SQL Data Manipulation Language (DML) statement, such as INSERT, UPDATE or DELETE; or an SQL statement that returns nothing, such as a DDL statement.

Returns: either (1) the row count for SQL Data Manipulation Language (DML) statements or (2) 0 for SQL statements that return nothing