Emprunter un livre

private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                         

          try {
          int nb=0;/*nombre des livres disponbles*/
          int nb1=0;/*nombre des livre empruntés par un étudiant*/
            
          String mysql = "select nbrlivemp  from tableuser where iduser=?"; 
          String idu = idus.getText();
          
          pst = conn.prepareStatement(mysql);
          pst.setString(1, idu);
          rs = pst.executeQuery();
          while (rs.next()) {
          nb = rs.getInt("nbrlivemp");
          }
          if (nb==0){
          
            
            
            String mysql1="select nbLivDispo  from tableliv where idliv=?";
            String idL= idli.getText();
            pst1 = conn.prepareStatement(mysql1 );
            pst1.setString(2, idL);
              
            rs1 = pst1.executeQuery();
            while (rs1.next()) {
              nb1 = rs1.getInt("nbLivDispo");
                
            }  
            if (nb1 >=1) {
                nb++;
                nb1--;
                String val = String.valueOf(nb);
                String val1 = String.valueOf(nb1);
                String mysql2="update tableuser set nbrlivemp='"+val+"' where iduser=?";
                
                pst2= conn.prepareStatement(mysql2);
                 
                pst2.setString(1, idu);
                pst2.executeUpdate();
                String mysql3="update tableliv set nbLivDispo='"+val1+"' where idliv=?";
                
                pst3 = conn.prepareStatement(mysql3);
                 
                pst3.setString(2, idL);
                pst3.executeUpdate();
                
                JOptionPane.showMessageDialog(this, "livre bien emprunté "
                ,"Bien", JOptionPane.PLAIN_MESSAGE);
            }
                 
            else {  
                JOptionPane.showMessageDialog(this, "Pas de livre disponible"
                ,"livre 0 ", JOptionPane.PLAIN_MESSAGE);
            }
          }
          else{
              JOptionPane.showMessageDialog(this, "c'est suffisant  pour vous  SVP!!"
                ,"c suffisan pr vous !!", JOptionPane.PLAIN_MESSAGE);
              
          }
          }catch (Exception  ex) {
            Logger.getLogger(PreRen.class.getName()).log(Level.SEVERE, null, ex);

    }