您实际上并没有在设置员中“设置”任何东西。
public void setFirstName(String firstName){ try{ // Here you create a READing statement. statement= con.prepareStatement("SELECt * FROM guest WHERe firstName = ?"); statement.setString(1, firstName); ResultSet rs = statement.executeQuery(); while(rs.next()){ // Here you set the >>method param<< to a non-existing String firstName = rs.getString(1); } }catch(Exception e){ System.out.print(e); }}// After the method is done you have done nothing because you didn't even set your class member variable "firstName", which you would have set using "this.firstName".最重要的是：我对getter和setter的理解使您可以在getter中进行查询。
