001/*
002 *  Copyright 2001-2005 Stephen Colebourne
003 *
004 *  Licensed under the Apache License, Version 2.0 (the "License");
005 *  you may not use this file except in compliance with the License.
006 *  You may obtain a copy of the License at
007 *
008 *      http://www.apache.org/licenses/LICENSE-2.0
009 *
010 *  Unless required by applicable law or agreed to in writing, software
011 *  distributed under the License is distributed on an "AS IS" BASIS,
012 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 *  See the License for the specific language governing permissions and
014 *  limitations under the License.
015 */
016package org.joda.time;
017
018/**
019 * Defines a partial time that does not support every datetime field, and is
020 * thus a local time.
021 * <p>
022 * A <code>ReadablePartial</code> supports a subset of those fields on the chronology.
023 * It cannot be compared to a <code>ReadableInstant</code>, as it does not fully
024 * specify an instant in time. The time it does specify is a local time, and does
025 * not include a time zone.
026 * <p>
027 * A <code>ReadablePartial</code> can be converted to a <code>ReadableInstant</code>
028 * using the <code>toDateTime</code> method. This works by providing a full base
029 * instant that can be used to 'fill in the gaps' and specify a time zone.
030 *
031 * @author Stephen Colebourne
032 * @since 1.0
033 */
034public interface ReadablePartial {
035
036    /**
037     * Gets the number of fields that this partial supports.
038     *
039     * @return the number of fields supported
040     */
041    int size();
042
043    /**
044     * Gets the field type at the specified index.
045     *
046     * @param index  the index to retrieve
047     * @return the field at the specified index
048     * @throws IndexOutOfBoundsException if the index is invalid
049     */
050    DateTimeFieldType getFieldType(int index);
051
052    /**
053     * Gets the field at the specified index.
054     *
055     * @param index  the index to retrieve
056     * @return the field at the specified index
057     * @throws IndexOutOfBoundsException if the index is invalid
058     */
059    DateTimeField getField(int index);
060
061    /**
062     * Gets the value at the specified index.
063     *
064     * @param index  the index to retrieve
065     * @return the value of the field at the specified index
066     * @throws IndexOutOfBoundsException if the index is invalid
067     */
068    int getValue(int index);
069
070    /**
071     * Gets the chronology of the partial which is never null.
072     * <p>
073     * The {@link Chronology} is the calculation engine behind the partial and
074     * provides conversion and validation of the fields in a particular calendar system.
075     * 
076     * @return the chronology, never null
077     */
078    Chronology getChronology();
079
080    /**
081     * Gets the value of one of the fields.
082     * <p>
083     * The field type specified must be one of those that is supported by the partial.
084     *
085     * @param field  a DateTimeFieldType instance that is supported by this partial
086     * @return the value of that field
087     * @throws IllegalArgumentException if the field is null or not supported
088     */
089    int get(DateTimeFieldType field);
090
091    /**
092     * Checks whether the field type specified is supported by this partial.
093     *
094     * @param field  the field to check, may be null which returns false
095     * @return true if the field is supported
096     */
097    boolean isSupported(DateTimeFieldType field);
098
099    /**
100     * Converts this partial to a full datetime by resolving it against another
101     * datetime.
102     * <p>
103     * This method takes the specified datetime and sets the fields from this
104     * instant on top. The chronology from the base instant is used.
105     * <p>
106     * For example, if this partial represents a time, then the result of this
107     * method will be the datetime from the specified base instant plus the
108     * time from this partial.
109     *
110     * @param baseInstant  the instant that provides the missing fields, null means now
111     * @return the combined datetime
112     */
113    DateTime toDateTime(ReadableInstant baseInstant);
114
115    //-----------------------------------------------------------------------
116    /**
117     * Compares this partial with the specified object for equality based
118     * on the supported fields, chronology and values.
119     * <p>
120     * Two instances of ReadablePartial are equal if they have the same
121     * chronology, same field types (in same order) and same values.
122     *
123     * @param partial  the object to compare to
124     * @return true if equal
125     */
126    boolean equals(Object partial);
127
128    /**
129     * Gets a hash code for the partial that is compatible with the 
130     * equals method.
131     * <p>
132     * The formula used must be:
133     * <pre>
134     *  int total = 157;
135     *  for (int i = 0; i < fields.length; i++) {
136     *      total = 23 * total + values[i];
137     *      total = 23 * total + fieldTypes[i].hashCode();
138     *  }
139     *  total += chronology.hashCode();
140     *  return total;
141     * </pre>
142     *
143     * @return a suitable hash code
144     */
145    int hashCode();
146
147// NOTE: This method should have existed in Joda-Time v1.0.
148// We STRONGLY recommend that all implementations of ReadablePartial
149// implement this method, as per AbstractPartial.
150// The simplest way to do this is to extend AbstractPartial.
151// v2.0 of Joda-Time will include this method in this interface.
152//    //-----------------------------------------------------------------------
153//    /**
154//     * Compares this partial with another returning an integer
155//     * indicating the order.
156//     * <p>
157//     * The fields are compared in order, from largest to smallest.
158//     * The first field that is non-equal is used to determine the result.
159//     * Thus a YearHour partial will first be compared on the year, and then
160//     * on the hour.
161//     * <p>
162//     * The specified object must be a partial instance whose field types
163//     * match those of this partial. If the parial instance has different
164//     * fields then a ClassCastException is thrown.
165//     *
166//     * @param partial  an object to check against
167//     * @return negative if this is less, zero if equal, positive if greater
168//     * @throws ClassCastException if the partial is the wrong class
169//     *  or if it has field types that don't match
170//     * @throws NullPointerException if the partial is null
171//     * @since 2.0
172//     */
173//    int compareTo(Object partial);
174
175    //-----------------------------------------------------------------------
176    /**
177     * Get the value as a String in a recognisable ISO8601 format, only
178     * displaying supported fields.
179     * <p>
180     * The string output is in ISO8601 format to enable the String
181     * constructor to correctly parse it.
182     *
183     * @return the value as an ISO8601 string
184     */
185    String toString();
186
187}