Question

我需要Java中的ArrayList帮助。我花了很长时间调试，但仍然。问题是 - 我将一些数据从数据库保存到字符串数组并将此数组保存到ArrayList，在输出中它只保存最后一个元素多次。看起来它只是重写它。

String[] result=new String[2];
String userId=Personal_Organizer.userProfile.getUserID();
ArrayList<Object> params = new ArrayList<Object>();           
params.add(userId);
String query1 = "select * from tblMemos where "
        + "_user_id = ?";

int rows;
System.out.println(query1);
executeQueryP(query1, params);

ArrayList<String[]> fetched = new ArrayList<String[]>();
int i=0;

try {
    while(rs.next()) {

        result[0] = rs.getString(2);
        result[1] = rs.getString(3);

        System.out.print("Counter: "+i);
        try{
            fetched.add(i,result);//here tried just .add(result) and output is same.
            i++;
        }catch(Exception e){
            System.out.println("Exceptional exception "+e);
        }

    }
    // Just to check. I have 2 records in DB and it shows last record twice 
    System.out.println(fetched.size());
    System.out.println(fetched.get(0)[0]);
    System.out.println(fetched.get(1)[0]);
}
// ...

Answer 1

您必须在每次迭代中创建一个新的数组实例：

while(rs.next()) {
    result = new String[2];
    result[0] = rs.getString(2);
    result[1] = rs.getString(3);
    fetched.add(result);
}

否则，您将多次向List添加相同的数组实例，并且每次迭代都会使用最新数据覆盖该数组的内容。

String Arrays的ArrayList仅保存最后一条记录

1 个答案: