001/*
002 *  Copyright 2001-2011 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} supports a subset of those fields on the chronology.
023 * It cannot be compared to a {@code ReadableInstant}, 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} can be converted to a {@code ReadableInstant}
028 * using the {@code toDateTime} 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 * <p>
031 * {@code ReadablePartial} is {@code Comparable} from v2.0.
032 * The comparison is based on the fields, compared in order, from largest to smallest.
033 * The first field that is non-equal is used to determine the result.
034 *
035 * @author Stephen Colebourne
036 * @since 1.0
037 */
038public interface ReadablePartial extends Comparable<ReadablePartial> {
039
040    /**
041     * Gets the number of fields that this partial supports.
042     *
043     * @return the number of fields supported
044     */
045    int size();
046
047    /**
048     * Gets the field type at the specified index.
049     *
050     * @param index  the index to retrieve
051     * @return the field at the specified index
052     * @throws IndexOutOfBoundsException if the index is invalid
053     */
054    DateTimeFieldType getFieldType(int index);
055
056    /**
057     * Gets the field at the specified index.
058     *
059     * @param index  the index to retrieve
060     * @return the field at the specified index
061     * @throws IndexOutOfBoundsException if the index is invalid
062     */
063    DateTimeField getField(int index);
064
065    /**
066     * Gets the value at the specified index.
067     *
068     * @param index  the index to retrieve
069     * @return the value of the field at the specified index
070     * @throws IndexOutOfBoundsException if the index is invalid
071     */
072    int getValue(int index);
073
074    /**
075     * Gets the chronology of the partial which is never null.
076     * <p>
077     * The {@link Chronology} is the calculation engine behind the partial and
078     * provides conversion and validation of the fields in a particular calendar system.
079     * 
080     * @return the chronology, never null
081     */
082    Chronology getChronology();
083
084    /**
085     * Gets the value of one of the fields.
086     * <p>
087     * The field type specified must be one of those that is supported by the partial.
088     *
089     * @param field  a DateTimeFieldType instance that is supported by this partial
090     * @return the value of that field
091     * @throws IllegalArgumentException if the field is null or not supported
092     */
093    int get(DateTimeFieldType field);
094
095    /**
096     * Checks whether the field type specified is supported by this partial.
097     *
098     * @param field  the field to check, may be null which returns false
099     * @return true if the field is supported
100     */
101    boolean isSupported(DateTimeFieldType field);
102
103    /**
104     * Converts this partial to a full datetime by resolving it against another
105     * datetime.
106     * <p>
107     * This method takes the specified datetime and sets the fields from this
108     * instant on top. The chronology from the base instant is used.
109     * <p>
110     * For example, if this partial represents a time, then the result of this
111     * method will be the datetime from the specified base instant plus the
112     * time from this partial.
113     *
114     * @param baseInstant  the instant that provides the missing fields, null means now
115     * @return the combined datetime
116     */
117    DateTime toDateTime(ReadableInstant baseInstant);
118
119    //-----------------------------------------------------------------------
120    /**
121     * Compares this partial with the specified object for equality based
122     * on the supported fields, chronology and values.
123     * <p>
124     * Two instances of ReadablePartial are equal if they have the same
125     * chronology, same field types (in same order) and same values.
126     *
127     * @param partial  the object to compare to
128     * @return true if equal
129     */
130    boolean equals(Object partial);
131
132    /**
133     * Gets a hash code for the partial that is compatible with the 
134     * equals method.
135     * <p>
136     * The formula used must be:
137     * <pre>
138     *  int total = 157;
139     *  for (int i = 0; i < fields.length; i++) {
140     *      total = 23 * total + values[i];
141     *      total = 23 * total + fieldTypes[i].hashCode();
142     *  }
143     *  total += chronology.hashCode();
144     *  return total;
145     * </pre>
146     *
147     * @return a suitable hash code
148     */
149    int hashCode();
150
151    //-----------------------------------------------------------------------
152//  This is commented out to improve backwards compatibility
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 year-hour 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 partial instance has different
164//     * fields then a {@code 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, previously on {@code AbstractPartial}
172//     */
173//    int compareTo(ReadablePartial 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}