Multiple query results in HashMap

Question

Hi,
Can anybody tell me how I can store multiple results of a select query in a HashMap. I basically know how to do it but here is the problem:
I want the table ids to be the keys and ArraySets containing database data to be the values of the HashMap. But whenever I add a new key/value pair to the HashMap all the values get overridden with the ArraySet I add.
Here is my code:
public HashMap getResults() throws Exception {
Class.forName(org.gjt.mm.mysql.Driver);
Connection con = DriverManager.getConnection(jdbc:mysql:///myDbName?user=user&password=password);
HashMap hmResults = new HashMap();
ArrayList alValues = new ArrayList();
PreparedStatement preparedStatement = con.prepareStatement("select id, name, email from mytable");
ResultSet resultSet = preparedStatement.executeQuery();
if (resultSet != null) {
while (resultSet.next()) {
alValues.clear();
alValues.add(resultSet.getString("id"));
alValues.add(resultSet.getString("name"));
alValues.add(resultSet.getString("email"));
// the next line adds the correct key and value but also overrides all the other values in the HashMap, why?
hmResults.put(resultSet.getString("id"), alValues);
return(hmResults);
The method above returns a HashMap containing the correct keys but the values are all the same.
What am I doing wrong?
Thanks for helping me out!

Answer 1

Because your adding to the HashMap a reference to that ArrayList, not the ArrayList itself. So basically each key in your HashMap references the one ArrayList, which you repeatedly clear and update. In the end, all your keys map to the same reference, which will contain the very last information retrieved from the ResultSet.
Simple fix... place the ArrayList alValues = new ArrayList() line inside your loop, and each key will be mapped to a different reference.