1 /*
   2  * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 /*
  27  * This file is available under and governed by the GNU General Public
  28  * License version 2 only, as published by the Free Software Foundation.
  29  * However, the following notice accompanied the original version of this
  30  * file:
  31  *
  32  * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
  33  *
  34  * All rights reserved.
  35  *
  36  * Redistribution and use in source and binary forms, with or without
  37  * modification, are permitted provided that the following conditions are met:
  38  *
  39  *  * Redistributions of source code must retain the above copyright notice,
  40  *    this list of conditions and the following disclaimer.
  41  *
  42  *  * Redistributions in binary form must reproduce the above copyright notice,
  43  *    this list of conditions and the following disclaimer in the documentation
  44  *    and/or other materials provided with the distribution.
  45  *
  46  *  * Neither the name of JSR-310 nor the names of its contributors
  47  *    may be used to endorse or promote products derived from this software
  48  *    without specific prior written permission.
  49  *
  50  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  51  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  52  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  53  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  54  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  55  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  56  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  57  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  58  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  59  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  60  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  61  */
  62 
  63 /**
  64  * <p>
  65  * Access to date and time using fields and units, additional value type classes and
  66  * base support for calendar systems other than the default ISO.
  67  * </p>
  68  * <p>
  69  * This package expands on the base package to provide additional functionality for
  70  * more powerful use cases. Support is included for:
  71  * </p>
  72  * <ul>
  73  * <li>Units of date-time, such as years, months, days and hours</li>
  74  * <li>Fields of date-time, such as month-of-year, day-of-week or hour-of-day</li>
  75  * <li>Date-time adjustment functions</li>
  76  * <li>Different definitions of weeks</li>
  77  * <li>Alternate calendar systems</li>
  78  * <li>Additional value types</li>
  79  * </ul>
  80  *
  81  * <h3>Fields and Units</h3>
  82  * <p>
  83  * Dates and times are expressed in terms of fields and units.
  84  * A unit is used to measure an amount of time, such as years, days or minutes.
  85  * All units implement {@link java.time.temporal.TemporalUnit}.
  86  * The set of well known units is defined in {@link java.time.temporal.ChronoUnit}, such as {@code DAYS}.
  87  * The unit interface is designed to allow applications defined units.
  88  * </p>
  89  * <p>
  90  * A field is used to express part of a larger date-time, such as year, month-of-year or second-of-minute.
  91  * All fields implement {@link java.time.temporal.TemporalField}.
  92  * The set of well known fields are defined in {@link java.time.temporal.ChronoField}, such as {@code HOUR_OF_DAY}.
  93  * Additional fields are defined by {@link java.time.temporal.JulianFields}, {@link java.time.temporal.WeekFields}
  94  * and {@link java.time.temporal.ISOFields}.
  95  * The field interface is designed to allow applications defined fields.
  96  * </p>
  97  * <p>
  98  * This package provides tools that allow the units and fields of date and time to be accessed
  99  * in a general way most suited for frameworks.
 100  * {@link java.time.temporal.Temporal} provides the abstraction for date time types that support fields.
 101  * Its methods support getting the value of a field, creating a new date time with the value of
 102  * a field modified, and querying for additional information, typically used to extract the offset or time-zone.
 103  * </p>
 104  * <p>
 105  * One use of fields in application code is to retrieve fields for which there is no convenience method.
 106  * For example, getting the day-of-month is common enough that there is a method on {@code LocalDate}
 107  * called {@code getDayOfMonth()}. However for more unusual fields it is necessary to use the field.
 108  * For example, {@code date.get(ChronoField.ALIGNED_WEEK_OF_MONTH)}.
 109  * The fields also provide access to the range of valid values.
 110  * </p>
 111  *
 112  * <h3>Adjustment and Query</h3>
 113  * <p>
 114  * A key part of the date-time problem space is adjusting a date to a new, related value,
 115  * such as the "last day of the month", or "next Wednesday".
 116  * These are modeled as functions that adjust a base date-time.
 117  * The functions implement {@link java.time.temporal.TemporalAdjuster} and operate on {@code Temporal}.
 118  * A set of common functions are provided in {@link java.time.temporal.Adjusters}.
 119  * For example, to find the first occurrence of a day-of-week after a given date, use
 120  * {@link java.time.temporal.Adjusters#next(DayOfWeek)}, such as
 121  * {@code date.with(next(MONDAY))}.
 122  * Applications can also define adjusters by implementing {@code TemporalAdjuster}.
 123  * </p>
 124  * <p>
 125  * There are additional interfaces to model addition to and subtraction from a date-time.
 126  * These are {@link java.time.temporal.TemporalAdder} and {@link java.time.temporal.TemporalSubtractor}.
 127  * </p>
 128  * <p>
 129  * In addition to adjusting a date-time, an interface is provided to enable querying -
 130  * {@link java.time.temporal.TemporalQuery}.
 131  * The most common implementations of the query interface are method references.
 132  * The {@code from(TemporalAccessor)} methods on major classes can all be used, such as
 133  * {@code LocalDate::from} or {@code Month::from}.
 134  * Further implementations are provided in {@link java.time.temporal.Queries}.
 135  * Applications can also define queries by implementing {@code TemporalQuery}.
 136  * </p>
 137  *
 138  * <h3>Weeks</h3>
 139  * <p>
 140  * Different locales have different definitions of the week.
 141  * For example, in Europe the week typically starts on a Monday, while in the US it starts on a Sunday.
 142  * The {@link java.time.temporal.WeekFields} class models this distinction.
 143  * </p>
 144  * <p>
 145  * The ISO calendar system defines an additional week-based division of years.
 146  * This defines a year based on whole Monday to Monday weeks.
 147  * This is modeled in {@link java.time.temporal.ISOFields}.
 148  * </p>
 149  *
 150  * <h3>Alternate calendar systems</h3>
 151  * <p>
 152  * The main API is based around the calendar system defined in ISO-8601.
 153  * However, there are other calendar systems, and this package provides basic support for them.
 154  * The alternate calendars are provided in the {@code java.time.calendar} package.
 155  * </p>
 156  * <p>
 157  * A calendar system is defined by the {@link java.time.temporal.Chrono} interface,
 158  * while a date in a calendar system is defined by the {@link java.time.temporal.ChronoLocalDate} interface.
 159  * </p>
 160  * <p>
 161  * It is intended that applications use the main API whenever possible, including code to read and write
 162  * from a persistent data store, such as a database, and to send dates and times across a network.
 163  * The "chrono" classes are then used at the user interface level to deal with localized input/output.
 164  * </p>
 165  * <p>
 166  * Using non-ISO calendar systems in an application introduces significant extra complexity.
 167  * Ensure that the warnings and recommendations in {@code ChronoLocalDate} have been read before
 168  * working with the "chrono" interfaces.
 169  * </p>
 170  * <p>
 171  * This example creates and uses a date in a non-ISO calendar system.
 172  * </p>
 173  * <pre>
 174  *   // Print the Thai Buddhist date
 175  *       ChronoLocalDate&lt;ThaiBuddhistChrono&gt; now1 = ThaiBuddhistChrono.INSTANCE.dateNow();
 176  *       int day = now1.get(ChronoField.DAY_OF_MONTH);
 177  *       int dow = now1.get(ChronoField.DAY_OF_WEEK);
 178  *       int month = now1.get(ChronoField.MONTH_OF_YEAR);
 179  *       int year = now1.get(ChronoField.YEAR);
 180  *       System.out.printf("  Today is %s %s %d-%s-%d%n", now1.getChrono().getId(),
 181  *                 dow, day, month, year);
 182  *
 183  *   // Enumerate the list of available calendars and print today for each
 184  *       Set&lt;Chrono&lt;?&gt;&gt; chronos = Chrono.getAvailableChronologies();
 185  *       for (Chrono&lt;?&gt; chrono : chronos) {
 186  *         ChronoLocalDate&lt;?&gt; date = chrono.dateNow();
 187  *         System.out.printf("   %20s: %s%n", chrono.getId(), date.toString());
 188  *       }
 189  *
 190  *   // Print today's date and the last day of the year for the Thai Buddhist Calendar.
 191  *       ChronoLocalDate&lt;ThaiBuddhistChrono&gt; first = now1
 192  *                 .with(ChronoField.DAY_OF_MONTH, 1)
 193  *                 .with(ChronoField.MONTH_OF_YEAR, 1);
 194  *       ChronoLocalDate&lt;ThaiBuddhistChrono&gt; last = first
 195  *                 .plus(1, ChronoUnit.YEARS)
 196  *                 .minus(1, ChronoUnit.DAYS);
 197  *       System.out.printf("  %s: 1st of year: %s; end of year: %s%n", last.getChrono().getId(),
 198  *                 first, last);
 199  *  </pre>
 200  *
 201  * <h3>Package specification</h3>
 202  * <p>
 203  * Unless otherwise noted, passing a null argument to a constructor or method in any class or interface
 204  * in this package will cause a {@link java.lang.NullPointerException NullPointerException} to be thrown.
 205  * The Javadoc "@param" definition is used to summarise the null-behavior.
 206  * The "@throws {@link java.lang.NullPointerException}" is not explicitly documented in each method.
 207  * </p>
 208  * <p>
 209  * All calculations should check for numeric overflow and throw either an {@link java.lang.ArithmeticException}
 210  * or a {@link java.time.DateTimeException}.
 211  * </p>
 212  * @since JDK1.8
 213  */
 214 package java.time.temporal;