Here you can find the source of getDaysInMonth(int year, int month)
public static int getDaysInMonth(int year, int month)
//package com.java2s; /*//from w ww .j av a 2 s .c om * Copyright (c) 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015 David Berkman * * This file is part of the SmallMind Code Project. * * The SmallMind Code Project is free software, you can redistribute * it and/or modify it under the terms of GNU Affero General Public * License as published by the Free Software Foundation, either version 3 * of the License, or (at your option) any later version. * * The SmallMind Code Project 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 * General Public License for more details. * * You should have received a copy of the the GNU Affero General Public * License, along with the SmallMind Code Project. If not, see * <http://www.gnu.org/licenses/>. * * Additional permission under the GNU Affero GPL version 3 section 7 * ------------------------------------------------------------------ * If you modify this Program, or any covered work, by linking or * combining it with other code, such other code is not for that reason * alone subject to any of the requirements of the GNU Affero GPL * version 3. */ public class Main { private static final int[] DAYS_IN_MONTH = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }; public static int getDaysInMonth(int year, int month) { if (month == 2) { if ((year % 4) == 0) { return 29; } } return DAYS_IN_MONTH[month - 1]; } }