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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   *
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37   * modification, are permitted provided that the following conditions are met:
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62  package java.time.temporal;
63  
64  import java.time.DateTimeException;
65  import java.util.Objects;
66  
67  /**
68   * Framework-level interface defining read-only access to a temporal object,
69   * such as a date, time, offset or some combination of these.
70   * <p>
71   * This is the base interface type for date, time and offset objects.
72   * It is implemented by those classes that can provide information
73   * as {@linkplain TemporalField fields} or {@linkplain TemporalQuery queries}.
74   * <p>
75   * Most date and time information can be represented as a number.
76   * These are modeled using {@code TemporalField} with the number held using
77   * a {@code long} to handle large values. Year, month and day-of-month are
78   * simple examples of fields, but they also include instant and offsets.
79   * See {@link ChronoField} for the standard set of fields.
80   * <p>
81   * Two pieces of date/time information cannot be represented by numbers,
82   * the {@linkplain java.time.chrono.Chronology chronology} and the
83   * {@linkplain java.time.ZoneId time-zone}.
84   * These can be accessed via {@linkplain #query(TemporalQuery) queries} using
85   * the static methods defined on {@link TemporalQuery}.
86   * <p>
87   * A sub-interface, {@link Temporal}, extends this definition to one that also
88   * supports adjustment and manipulation on more complete temporal objects.
89   * <p>
90   * This interface is a framework-level interface that should not be widely
91   * used in application code. Instead, applications should create and pass
92   * around instances of concrete types, such as {@code LocalDate}.
93   * There are many reasons for this, part of which is that implementations
94   * of this interface may be in calendar systems other than ISO.
95   * See {@link java.time.chrono.ChronoLocalDate} for a fuller discussion of the issues.
96   *
97   * @implSpec
98   * This interface places no restrictions on the mutability of implementations,
99   * however immutability is strongly recommended.
100  *
101  * @since 1.8
102  */
103 public interface TemporalAccessor {
104 
105     /**
106      * Checks if the specified field is supported.
107      * <p>
108      * This checks if the date-time can be queried for the specified field.
109      * If false, then calling the {@link #range(TemporalField) range} and {@link #get(TemporalField) get}
110      * methods will throw an exception.
111      *
112      * @implSpec
113      * Implementations must check and handle all fields defined in {@link ChronoField}.
114      * If the field is supported, then true must be returned, otherwise false must be returned.
115      * <p>
116      * If the field is not a {@code ChronoField}, then the result of this method
117      * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
118      * passing {@code this} as the argument.
119      * <p>
120      * Implementations must ensure that no observable state is altered when this
121      * read-only method is invoked.
122      *
123      * @param field  the field to check, null returns false
124      * @return true if this date-time can be queried for the field, false if not
125      */
126     boolean isSupported(TemporalField field);
127 
128     /**
129      * Gets the range of valid values for the specified field.
130      * <p>
131      * All fields can be expressed as a {@code long} integer.
132      * This method returns an object that describes the valid range for that value.
133      * The value of this temporal object is used to enhance the accuracy of the returned range.
134      * If the date-time cannot return the range, because the field is unsupported or for
135      * some other reason, an exception will be thrown.
136      * <p>
137      * Note that the result only describes the minimum and maximum valid values
138      * and it is important not to read too much into them. For example, there
139      * could be values within the range that are invalid for the field.
140      *
141      * @implSpec
142      * Implementations must check and handle all fields defined in {@link ChronoField}.
143      * If the field is supported, then the range of the field must be returned.
144      * If unsupported, then an {@code UnsupportedTemporalTypeException} must be thrown.
145      * <p>
146      * If the field is not a {@code ChronoField}, then the result of this method
147      * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessorl)}
148      * passing {@code this} as the argument.
149      * <p>
150      * Implementations must ensure that no observable state is altered when this
151      * read-only method is invoked.
152      * <p>
153      * The default implementation must behave equivalent to this code:
154      * <pre>
155      *  if (field instanceof ChronoField) {
156      *    if (isSupported(field)) {
157      *      return field.range();
158      *    }
159      *    throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
160      *  }
161      *  return field.rangeRefinedBy(this);
162      * </pre>
163      *
164      * @param field  the field to query the range for, not null
165      * @return the range of valid values for the field, not null
166      * @throws DateTimeException if the range for the field cannot be obtained
167      * @throws UnsupportedTemporalTypeException if the field is not supported
168      */
169     default ValueRange range(TemporalField field) {
170         if (field instanceof ChronoField) {
171             if (isSupported(field)) {
172                 return field.range();
173             }
174             throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
175         }
176         Objects.requireNonNull(field, "field");
177         return field.rangeRefinedBy(this);
178     }
179 
180     /**
181      * Gets the value of the specified field as an {@code int}.
182      * <p>
183      * This queries the date-time for the value for the specified field.
184      * The returned value will always be within the valid range of values for the field.
185      * If the date-time cannot return the value, because the field is unsupported or for
186      * some other reason, an exception will be thrown.
187      *
188      * @implSpec
189      * Implementations must check and handle all fields defined in {@link ChronoField}.
190      * If the field is supported and has an {@code int} range, then the value of
191      * the field must be returned.
192      * If unsupported, then an {@code UnsupportedTemporalTypeException} must be thrown.
193      * <p>
194      * If the field is not a {@code ChronoField}, then the result of this method
195      * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
196      * passing {@code this} as the argument.
197      * <p>
198      * Implementations must ensure that no observable state is altered when this
199      * read-only method is invoked.
200      * <p>
201      * The default implementation must behave equivalent to this code:
202      * <pre>
203      *  if (range(field).isIntValue()) {
204      *    return range(field).checkValidIntValue(getLong(field), field);
205      *  }
206      *  throw new UnsupportedTemporalTypeException("Invalid field " + field + " + for get() method, use getLong() instead");
207      * </pre>
208      *
209      * @param field  the field to get, not null
210      * @return the value for the field, within the valid range of values
211      * @throws DateTimeException if a value for the field cannot be obtained or
212      *         the value is outside the range of valid values for the field
213      * @throws UnsupportedTemporalTypeException if the field is not supported or
214      *         the range of values exceeds an {@code int}
215      * @throws ArithmeticException if numeric overflow occurs
216      */
217     default int get(TemporalField field) {
218         ValueRange range = range(field);
219         if (range.isIntValue() == false) {
220             throw new UnsupportedTemporalTypeException("Invalid field " + field + " + for get() method, use getLong() instead");
221         }
222         long value = getLong(field);
223         if (range.isValidValue(value) == false) {
224             throw new DateTimeException("Invalid value for " + field + " (valid values " + range + "): " + value);
225         }
226         return (int) value;
227     }
228 
229     /**
230      * Gets the value of the specified field as a {@code long}.
231      * <p>
232      * This queries the date-time for the value for the specified field.
233      * The returned value may be outside the valid range of values for the field.
234      * If the date-time cannot return the value, because the field is unsupported or for
235      * some other reason, an exception will be thrown.
236      *
237      * @implSpec
238      * Implementations must check and handle all fields defined in {@link ChronoField}.
239      * If the field is supported, then the value of the field must be returned.
240      * If unsupported, then an {@code UnsupportedTemporalTypeException} must be thrown.
241      * <p>
242      * If the field is not a {@code ChronoField}, then the result of this method
243      * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
244      * passing {@code this} as the argument.
245      * <p>
246      * Implementations must ensure that no observable state is altered when this
247      * read-only method is invoked.
248      *
249      * @param field  the field to get, not null
250      * @return the value for the field
251      * @throws DateTimeException if a value for the field cannot be obtained
252      * @throws UnsupportedTemporalTypeException if the field is not supported
253      * @throws ArithmeticException if numeric overflow occurs
254      */
255     long getLong(TemporalField field);
256 
257     /**
258      * Queries this date-time.
259      * <p>
260      * This queries this date-time using the specified query strategy object.
261      * <p>
262      * Queries are a key tool for extracting information from date-times.
263      * They exists to externalize the process of querying, permitting different
264      * approaches, as per the strategy design pattern.
265      * Examples might be a query that checks if the date is the day before February 29th
266      * in a leap year, or calculates the number of days to your next birthday.
267      * <p>
268      * The most common query implementations are method references, such as
269      * {@code LocalDate::from} and {@code ZoneId::from}.
270      * Additional implementations are provided as static methods on {@link TemporalQuery}.
271      *
272      * @implSpec
273      * The default implementation must behave equivalent to this code:
274      * <pre>
275      *  if (query == TemporalQueries.zoneId() ||
276      *        query == TemporalQueries.chronology() || query == TemporalQueries.precision()) {
277      *    return null;
278      *  }
279      *  return query.queryFrom(this);
280      * </pre>
281      * Future versions are permitted to add further queries to the if statement.
282      * <p>
283      * All classes implementing this interface and overriding this method must call
284      * {@code TemporalAccessor.super.query(query)}. JDK classes may avoid calling
285      * super if they provide behavior equivalent to the default behaviour, however
286      * non-JDK classes may not utilize this optimization and must call {@code super}.
287      * <p>
288      * If the implementation can supply a value for one of the queries listed in the
289      * if statement of the default implementation, then it must do so.
290      * For example, an application-defined {@code HourMin} class storing the hour
291      * and minute must override this method as follows:
292      * <pre>
293      *  if (query == TemporalQueries.precision()) {
294      *    return MINUTES;
295      *  }
296      *  return TemporalAccessor.super.query(query);
297      * </pre>
298      * <p>
299      * Implementations must ensure that no observable state is altered when this
300      * read-only method is invoked.
301      *
302      * @param <R> the type of the result
303      * @param query  the query to invoke, not null
304      * @return the query result, null may be returned (defined by the query)
305      * @throws DateTimeException if unable to query
306      * @throws ArithmeticException if numeric overflow occurs
307      */
308     default <R> R query(TemporalQuery<R> query) {
309         if (query == TemporalQueries.zoneId()
310                 || query == TemporalQueries.chronology()
311                 || query == TemporalQueries.precision()) {
312             return null;
313         }
314         return query.queryFrom(this);
315     }
316 
317 }