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    <p>Because you're hauling the <strong>entire</strong> database table down into Java's memory and testing <em>every</em> row in a while loop. You don't break the loop if a match is found so that it continues overwriting the boolean outcome until with the last row.</p> <p>That said, you really don't want to do the comparison in Java. Just make use of the <a href="http://www.w3schools.com/SQl/sql_where.asp" rel="nofollow noreferrer">SQL <code>WHERE</code> clause</a>. That's <em>much</em> more efficient and really the task a DB is supposed to do. Don't try to take over the DB's work in Java, it's only going to be inefficient.</p> <pre><code>public boolean exists(String username, String password) throws SQLException { Connection connection = null; PreparedStatement preparedStatement = null; ResultSet resultSet = null; boolean exists = false; try { connection = database.getConnection(); preparedStatement = connection.prepareStatement("SELECT id FROM client WHERE username = ? AND password = ?"); preparedStatement.setString(1, username); preparedStatement.setString(2, password); resultSet = preparedStatement.executeQuery(); exists = resultSet.next(); } finally { close(resultSet); close(preparedStatement); close(connection); } return exists; } </code></pre> <p>You see that I made a few enhancements:</p> <ol> <li>Use preparedstatement.</li> <li>Do not use equalsignorecase. A password of "FooBar" should NOT be the same as "foobar".</li> <li>Gently acquire and close resources in same scope to avoid leaking.</li> <li>Have it in an independent and reuseable non-static DAO method.</li> </ol> <p>To learn more about using JDBC the proper way you may find <a href="http://balusc.blogspot.com/2008/07/dao-tutorial-data-layer.html" rel="nofollow noreferrer">this basic tutorial</a> useful.</p>
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    1. COthink we might need a bit more information than it doesn't work correctly... @BalusC's answer is about as good as it's going to get with the information you have provided
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    2. CO@Johanna: Then the problem lies somewhere else. Debug it. If you mean that `false` is been returned, then it simply means that there's no match in the DB :) By the way, your edited code is in JDBC perspective still wrong. You're still leaking the `Connection` and not closing the resources each in its own try-catch (and worse, the whole method is still `static`). Your app might break sooner or later when used extensively in production.
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    3. CO@Johanna: if you want more assistance, you really, *really* need to learn to ask questions the smart way. Plain saying "it doesn't work!" gives us really **nothing** to work with. Elaborate in detail what exactly happens and also elaborate in detail what exactly happens **not** (i.e. your expectations). With in detail, I mean at code (developer) level and not at end-user level.
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