java - 我在以下 SQL 子句中收到错误

Question

Exception in thread "main" java.lang.ClassCastException: org.apache.derby.client.am.Statement cannot be cast to java.beans.Statement
        at CollegeLibrary.NotRegistered.DBStatement(NotRegistered.java:114)
        at CollegeLibrary.NotRegistered.<init>(NotRegistered.java:85)
        at CollegeLibrary.NotRegistered.main(NotRegistered.java:91)
Java Result: 1

在这些部分中有错误

 ResultSet SelectQuery(Statement st) {
        ResultSet rs = null;
        try {
            rs = st.executeQuery("select * from APP.STUDENT");
        } catch (SQLException ex) {
            Logger.getLogger(NotRegistered.class.getName()).log(Level.SEVERE, null, ex);
        }
        return rs;
    }


    void InsertQuery(Statement st) {

        try {
            if(_txtFname.getText().length()>0 & _txtLname.getText().length()>0& _txtAddress.getText().length()>0&_txtPhone.getText().length()>0&_txtDob.getText().length()>0&_txtSTcode.getText().length()>0){

    st.executeQuery("insert into APP.STUDENT values ('"+_txtFname.getText()+"','"+_txtLname.getText()+"','"+_txtAddress.getText()+"','"+_txtPhone.getText()+"','"+_txtDob.getText()+"','"+_txtSTcode.getText()+"')");
            }else{
                System.out.println("please fill up the form");
            }
              } catch (SQLException ex) {
            Logger.getLogger(NotRegistered.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
void  UpdateQuery(Statement st) {

        try {
            if(_txtFname.getText().length()>0 & _txtLname.getText().length()>0){
            st.executeUpdate("update APP.STUDENT SET USERNAME='"+_txtFname.getText()+
                    "', PASSWORD='"+_txtLname.getText()
                    +"' where USERNAME='"+_oldData+"'");
            }else{
                System.out.println("please fill up the form");
            }
              } catch (SQLException ex) {
            Logger.getLogger(NotRegistered.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
void  DeleteQuery(Statement st) {

        try {
            if(_txtFname.getText().length()>0 & _txtLname.getText().length()>0& _txtAddress.getText().length()>0&_txtPhone.getText().length()>0&_txtDob.getText().length()>0&_txtSTcode.getText().length()>0){
                System.out.println(" ");
            st.executeUpdate("delete from APP.STUDENT where USERNAME='"+_oldData+"'");
            }else{
                System.out.println("please fill up the form");
            }
              } catch (SQLException ex) {
            Logger.getLogger(NotRegistered.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Answer 1

java.lang.ClassCastException: org.apache.derby.client.am.Statement cannot be cast to java.beans.Statement

我认为您的代码中有错误的 import 语句。

有java.sql.Statement (你在这里想要的)和java.beans.Statement (这是完全不同的东西)。

在大多数情况下，您要使用 java.sql.PreparedStatement相反，无论如何，这也是绕过名称冲突的步骤。不要将文字值直接放在 SQL 中，使用绑定(bind)变量。