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copied!<p>The <a href="http://java.sun.com/javase/6/docs/api/java/util/Calendar.html" rel="noreferrer"><code>Calendar</code></a> object has an <a href="http://java.sun.com/javase/6/docs/api/java/util/Calendar.html#add(int,%20int)" rel="noreferrer"><code>add</code></a> method which allows one to add or subtract values of a specified field.</p> <p>For example,</p> <pre><code>Calendar c = new GregorianCalendar(2009, Calendar.JANUARY, 1); c.add(Calendar.DAY_OF_MONTH, 1); </code></pre> <p>The constants for specifying the field can be found in the "Field Summary" of the <a href="http://java.sun.com/javase/6/docs/api/java/util/Calendar.html" rel="noreferrer"><code>Calendar</code></a> class.</p> <p>Just for future reference, <a href="http://java.sun.com/javase/6/docs/api/" rel="noreferrer">The Java API Specification</a> contains a lot of helpful information about how to use the classes which are part of the Java API.</p> <hr> <p><strong>Update:</strong></p> <blockquote> <p>I am getting the error found void but expected int, in 'newDay = startDate.add(5, 1);' What should I do?</p> </blockquote> <p>The <code>add</code> method does not return anything, therefore, trying to assign the result of calling <code>Calendar.add</code> is not valid.</p> <p>The compiler error indicates that one is trying to assign a <code>void</code> to a variable with the type of <code>int</code>. This is not valid, as one cannot assign "nothing" to an <code>int</code> variable.</p> <p>Just a guess, but perhaps this may be what is trying to be achieved:</p> <pre><code>// Get a calendar which is set to a specified date. Calendar calendar = new GregorianCalendar(2009, Calendar.JANUARY, 1); // Get the current date representation of the calendar. Date startDate = calendar.getTime(); // Increment the calendar's date by 1 day. calendar.add(Calendar.DAY_OF_MONTH, 1); // Get the current date representation of the calendar. Date endDate = calendar.getTime(); System.out.println(startDate); System.out.println(endDate); </code></pre> <p>Output:</p> <pre><code>Thu Jan 01 00:00:00 PST 2009 Fri Jan 02 00:00:00 PST 2009 </code></pre> <p>What needs to be considered is what <code>Calendar</code> actually is.</p> <p>A <code>Calendar</code> is not a representation of a date. It is a representation of a calendar, and where it is currently pointing at. In order to get a representation of where the calendar is pointing at at the moment, one should obtain a <a href="http://java.sun.com/javase/6/docs/api/java/util/Date.html" rel="noreferrer"><code>Date</code></a> from the <code>Calendar</code> using the <a href="http://java.sun.com/javase/6/docs/api/java/util/Calendar.html#getTime()" rel="noreferrer"><code>getTime</code></a> method.</p>

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