ArrayList 中的每个 String[] 都具有相同的值

Question

我正在尝试使用从数据字典中获取的信息来创建用于创建/替换多个视图的 Oracle SQL 脚本。

我已经设法通过 JDBC 驱动程序和对数据字典的查询建立了一个有效的数据库连接，它也可以正常工作并返回正确的值。

但是，在将查询的信息存储在 String 数组中时 - 然后将其添加到 String[] 的 ArrayList 中 - 似乎出现了问题，因为所有数组似乎在它们各自的索引位置具有相同的值，而我没有不知道为什么会这样。

这是我的代码，如果有人能发现错误，我将不胜感激：

public ArrayList<String[]>  getDataDictionary(ArrayList<String> dbInfo, String table) throws SQLException {

ArrayList<String[]> result = new ArrayList<String[]>();
String[] resultTemp = new String[2];

... connection variables (URL, User, Pass)
... get connection, etc.

try {
            Statement statement = con.createStatement();
            ResultSet rs = statement.executeQuery("SELECT COLUMN_NAME,DATA_TYPE FROM USER_TAB_COLUMNS WHERE TABLE_NAME = '" + table + "'");

            while (rs.next()) {
                resultTemp[0] = rs.getString("COLUMN_NAME");
                resultTemp[1] = rs.getString("DATA_TYPE");

                // database values
                System.out.println(rs.getString("COLUMN_NAME"));
                System.out.println(rs.getString("DATA_TYPE"));
                // array values
                System.out.println(resultTemp[0]);
                System.out.println(resultTemp[1]);

                //The above sout's return the proper values for each pass of the loop
                //This is what feels the strangest to me. The values are correct here, but when queried later they are wrong

                result.add(resultTemp);
            }

            String[] test = new String[2];

            // sout's return wrong values now, i.e. the value returned is always the same for all arrays queried in the ArrayList
            //I don't understand how that can be, because the correct values were added to the ArrayList a few lines above and now they are wrong with no changes made
            test = result.get(0);
            System.out.println(test[0]);
            System.out.println(test[1]);

            test = result.get(1);
            System.out.println(test[0]);
            System.out.println(test[1]);

            test = result.get(2);
            System.out.println(test[0]);
            System.out.println(test[1]);

            rs.close();
            statement.close();
            con.close();

            return result;  
} catch(Exception e)
        {
            e.printStackTrace();
            Alert alert = new Alert(Alert.AlertType.ERROR);
            alert.setTitle("Error!");
            alert.setHeaderText("Invalid SQL!");
            alert.setContentText("Please verify the information you provided!");
            alert.showAndWait();
            return null;
        }

Answer 1

您应该在循环内创建数组实例。

       while (rs.next()) {
            String[] resultTemp = new String[2];
            resultTemp[0] = rs.getString("COLUMN_NAME");
            resultTemp[1] = rs.getString("DATA_TYPE");
            ....

不这样做会导致同一数组被多次添加到result。

Answer 2

您在每个循环中存储对同一对象的引用。

您必须在每个 lopp 中创建一个新数组：

 while (rs.next()) {
      resultTemp = new String[2];

                resultTemp[0] = rs.getString("COLUMN_NAME");
                resultTemp[1] = rs.getString("DATA_TYPE");

                // database values
                System.out.println(rs.getString("COLUMN_NAME"));
                System.out.println(rs.getString("DATA_TYPE"));
                // array values
                System.out.println(resultTemp[0]);
                System.out.println(resultTemp[1]);

                //The above sout's return the proper values for each pass of the loop
                //This is what feels the strangest to me. The values are correct here, but when queried later they are wrong

                result.add(resultTemp);
            }

Answer 3

您正在覆盖同一个数组，String[] resultTemp = new String[2];

while (rs.next()) {
            String[] resultTemp = new String[2];
            resultTemp[0] = rs.getString("COLUMN_NAME");
            resultTemp[1] = rs.getString("DATA_TYPE");

在while 循环内初始化它。这样当你添加

result.add(resultTemp);

result 将在其中保存resultTemp[] 对象的列表。