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copied!<ol> <li><p><code>Date</code> is not tied to any calendar system used by human beings. It just represents point in time. Adding 30 days to <code>Date</code> makes no sense, it is like adding 20 to <em>red</em> color.</p></li> <li><p>Common approach of adding <code>1000 * 60 * 60 * 24</code> is wrong. You are adding 86400 seconds, but one day is not necessarily 86400 seconds long. It can be one hour longer or shorter due to <a href="/questions/tagged/dst" class="post-tag" title="show questions tagged 'dst'" rel="tag">dst</a>. It can be one second longer or shorter due to <em>leap seconds</em>.</p></li> <li><p>What you <em>should</em> do is converting <code>Date</code> into a <code>Calendar</code> (which actually represents some calendar system, like <code>GregorianCalendar</code>. Then simply add days:</p> <pre><code>Calendar calendar = new GregorianCalendar(/* remember about timezone! */); calendar.setTime(date); calendar.add(Calendar.DATE, 30); date = calendar.getTime(); </code></pre></li> <li><p>Use <a href="http://commons.apache.org/lang/api-2.5/org/apache/commons/lang/time/DateUtils.html#addDays%28java.util.Date,%20int%29"><code>DateUtils.addDays()</code></a> from Apache Commons Lang:</p> <pre><code>DateUtils.add(date, 30); </code></pre> <p>This does not violate what was written above, it converts to <code>Calendar</code> underneath.</p></li> <li><p>Or avoid this hell altogether and go for <a href="http://joda-time.sourceforge.net/">Joda Time</a>.</p></li> </ol>

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