Java tutorial
/* * Copyright 2001-2005 Stephen Colebourne * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.joda.time; /** * Defines a time period specified in terms of individual duration fields * such as years and days. * <p> * The implementation of this interface may be mutable or immutable. This * interface only gives access to retrieve data, never to change it. * <p> * Periods are split up into multiple fields, for example days and seconds. * Implementations are not required to evenly distribute the values across the fields. * The value for each field may be positive or negative. * <p> * When a time period is added to an instant, the effect is to add each field in turn. * For example, a time period could be defined as 3 months, 2 days and -1 hours. * In most circumstances this would be the same as 3 months, 1 day, and 23 hours. * However, when adding across a daylight savings boundary, a day may be 23 or 25 hours long. * Thus, the time period is always added field by field to the datetime. * <p> * Periods are independent of chronology, and can only be treated as durations * when paired with a time via an interval. * * @see ReadableDuration * @see ReadableInterval * @author Brian S O'Neill * @author Stephen Colebourne * @since 1.0 */ public interface ReadablePeriod { /** * Gets the period type that defines which fields are included in the period. * * @return the period type */ PeriodType getPeriodType(); /** * Gets the number of fields that this period supports. * * @return the number of fields supported */ int size(); /** * Gets the field type at the specified index. * * @param index the index to retrieve * @return the field at the specified index * @throws IndexOutOfBoundsException if the index is invalid */ DurationFieldType getFieldType(int index); /** * Gets the value at the specified index. * * @param index the index to retrieve * @return the value of the field at the specified index * @throws IndexOutOfBoundsException if the index is invalid */ int getValue(int index); /** * Gets the value of one of the fields. * <p> * If the field type specified is not supported by the period then zero * is returned. * * @param field the field type to query, null returns zero * @return the value of that field, zero if field not supported */ int get(DurationFieldType field); /** * Checks whether the field type specified is supported by this period. * * @param field the field to check, may be null which returns false * @return true if the field is supported */ boolean isSupported(DurationFieldType field); //----------------------------------------------------------------------- /** * Get this period as an immutable <code>Period</code> object. * <p> * This will either typecast this instance, or create a new <code>Period</code>. * * @return a Duration using the same field set and values */ Period toPeriod(); /** * Get this object as a <code>MutablePeriod</code>. * <p> * This will always return a new <code>MutablePeriod</code> with the same fields. * * @return a MutablePeriod using the same field set and values */ MutablePeriod toMutablePeriod(); //----------------------------------------------------------------------- /** * Compares this object with the specified object for equality based * on the value and type of each supported field. * All ReadablePeriod instances are accepted. * <p> * Note that a period of 1 day is not equal to a period of 24 hours, * nor is 1 hour equal to 60 minutes. Only periods with the same amount * in each field are equal. * <p> * This is because periods represent an abstracted definition of a time * period (eg. a day may not actually be 24 hours, it might be 23 or 25 * at daylight savings boundary). * <p> * To compare the actual duration of two periods, convert both to * {@link Duration}s, an operation that emphasises that the result may * differ according to the date you choose. * * @param readablePeriod a readable period to check against * @return true if all the field values and types are equal, false if * not or the period is null or of an incorrect type */ boolean equals(Object readablePeriod); /** * Gets a hash code for the period that is compatible with the equals method. * The hashcode is calculated as follows: * <pre> * int total = 17; * for (int i = 0; i < fields.length; i++) { * total = 27 * total + getValue(i); * total = 27 * total + getFieldType(i).hashCode(); * } * return total; * </pre> * * @return a hash code */ int hashCode(); //----------------------------------------------------------------------- /** * Gets the value as a String in the style of the ISO8601 duration format. * Technically, the output can breach the ISO specification as weeks may be included. * <p> * For example, "PT6H3M5S" represents 6 hours, 3 minutes, 5 seconds. * * @return the value as an ISO8601 style string */ String toString(); }