Question

我正在创建一种算法，该算法从数据库中删除字符串中的名称。我正在使用JDBC客户端来获取所有值并将它们保存在ArrayList中。但是由于某些原因，某些变量在离开while(resultset.next())循环后会失去其值

public void getAllReqInfo(){
    //ArrayList from the class "req"
    reqArrayList = new ArrayList<req>();
    try {
        Statement stmt = con.createStatement();
        String query = "SELECT * FROM req";
        ResultSet resultSet = stmt.executeQuery(query);

        while (resultSet.next()){
            //class with all the columns from the database
            req req = new req(resultSet.getInt("id"),
                              resultSet.getString("comments"));

        reqArrayList.add(req);

        //Comments != null
        System.out.println(reqArrayList.get(0).getComments());

        //Id != null
        System.out.println(reqArrayList.get(0).getId());


        } // End of while

        //Comments == null
        System.out.println(reqArrayList.get(0).getComments());

        //Id != null
        System.out.println(reqArrayList.get(0).getId());
    } catch (SQLException e) {
        e.printStackTrace();
    }
}

“ req”类是具有getter和setter方法的自动生成的类。

我不知道为什么无论如何我都会得到帮助

Answer 1

reqArrayList.get(0)

您只会在循环中和循环之后打印出第一个要求。

要倾销整个批次，请做

for (req myReq:reqArrayList){
    System.out.println(myReq.getId()+" "+myReq.getComments());
}

离开whileloop后，ArrayList类丢失变量

1 个答案: