Here you can find the source of getDaysInMonth(Calendar cal)
public static int getDaysInMonth(Calendar cal)
//package com.java2s; /**//from w w w . j a v a2 s. c o m * Copyright (c) 2000-2012 Liferay, Inc. All rights reserved. * * This library is free software; you can redistribute it and/or modify it under * the terms of the GNU Lesser General Public License as published by the Free * Software Foundation; either version 2.1 of the License, or (at your option) * any later version. * * This library is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more * details. */ import java.util.Calendar; public class Main { public static int getDaysInMonth(Calendar cal) { return getDaysInMonth(cal.get(Calendar.MONTH), cal.get(Calendar.YEAR)); } public static int getDaysInMonth(int month, int year) { month++; if ((month == 1) || (month == 3) || (month == 5) || (month == 7) || (month == 8) || (month == 10) || (month == 12)) { return 31; } else if ((month == 4) || (month == 6) || (month == 9) || (month == 11)) { return 30; } else { if (((year % 4) == 0) && ((year % 100) != 0) || ((year % 400) == 0)) { return 29; } else { return 28; } } } }