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26  /*
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32   * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
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62  package java.time.chrono;
63  
64  import static java.time.temporal.ChronoField.ERA;
65  import static java.time.temporal.ChronoUnit.ERAS;
66  
67  import java.time.DateTimeException;
68  import java.time.temporal.UnsupportedTemporalTypeException;
69  import java.time.format.DateTimeFormatterBuilder;
70  import java.time.format.TextStyle;
71  import java.time.temporal.ChronoField;
72  import java.time.temporal.Temporal;
73  import java.time.temporal.TemporalAccessor;
74  import java.time.temporal.TemporalAdjuster;
75  import java.time.temporal.TemporalField;
76  import java.time.temporal.TemporalQueries;
77  import java.time.temporal.TemporalQuery;
78  import java.time.temporal.ValueRange;
79  import java.util.Locale;
80  
81  /**
82   * An era of the time-line.
83   * <p>
84   * Most calendar systems have a single epoch dividing the time-line into two eras.
85   * However, some calendar systems, have multiple eras, such as one for the reign
86   * of each leader.
87   * In all cases, the era is conceptually the largest division of the time-line.
88   * Each chronology defines the Era's that are known Eras and a
89   * {@link Chronology#eras Chronology.eras} to get the valid eras.
90   * <p>
91   * For example, the Thai Buddhist calendar system divides time into two eras,
92   * before and after a single date. By contrast, the Japanese calendar system
93   * has one era for the reign of each Emperor.
94   * <p>
95   * Instances of {@code Era} may be compared using the {@code ==} operator.
96   *
97   * @implSpec
98   * This interface must be implemented with care to ensure other classes operate correctly.
99   * All implementations must be singletons - final, immutable and thread-safe.
100  * It is recommended to use an enum whenever possible.
101  *
102  * @since 1.8
103  */
104 public interface Era extends TemporalAccessor, TemporalAdjuster {
105 
106     /**
107      * Gets the numeric value associated with the era as defined by the chronology.
108      * Each chronology defines the predefined Eras and methods to list the Eras
109      * of the chronology.
110      * <p>
111      * All fields, including eras, have an associated numeric value.
112      * The meaning of the numeric value for era is determined by the chronology
113      * according to these principles:
114      * <ul>
115      * <li>The era in use at the epoch 1970-01-01 (ISO) has the value 1.
116      * <li>Later eras have sequentially higher values.
117      * <li>Earlier eras have sequentially lower values, which may be negative.
118      * </ul>
119      *
120      * @return the numeric era value
121      */
122     int getValue();
123 
124     //-----------------------------------------------------------------------
125     /**
126      * Checks if the specified field is supported.
127      * <p>
128      * This checks if this era can be queried for the specified field.
129      * If false, then calling the {@link #range(TemporalField) range} and
130      * {@link #get(TemporalField) get} methods will throw an exception.
131      * <p>
132      * If the field is a {@link ChronoField} then the query is implemented here.
133      * The {@code ERA} field returns true.
134      * All other {@code ChronoField} instances will return false.
135      * <p>
136      * If the field is not a {@code ChronoField}, then the result of this method
137      * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)}
138      * passing {@code this} as the argument.
139      * Whether the field is supported is determined by the field.
140      *
141      * @param field  the field to check, null returns false
142      * @return true if the field is supported on this era, false if not
143      */
144     @Override
145     default boolean isSupported(TemporalField field) {
146         if (field instanceof ChronoField) {
147             return field == ERA;
148         }
149         return field != null && field.isSupportedBy(this);
150     }
151 
152     /**
153      * Gets the range of valid values for the specified field.
154      * <p>
155      * The range object expresses the minimum and maximum valid values for a field.
156      * This era is used to enhance the accuracy of the returned range.
157      * If it is not possible to return the range, because the field is not supported
158      * or for some other reason, an exception is thrown.
159      * <p>
160      * If the field is a {@link ChronoField} then the query is implemented here.
161      * The {@code ERA} field returns the range.
162      * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
163      * <p>
164      * If the field is not a {@code ChronoField}, then the result of this method
165      * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)}
166      * passing {@code this} as the argument.
167      * Whether the range can be obtained is determined by the field.
168      * <p>
169      * The default implementation must return a range for {@code ERA} from
170      * zero to one, suitable for two era calendar systems such as ISO.
171      *
172      * @param field  the field to query the range for, not null
173      * @return the range of valid values for the field, not null
174      * @throws DateTimeException if the range for the field cannot be obtained
175      * @throws UnsupportedTemporalTypeException if the unit is not supported
176      */
177     @Override  // override for Javadoc
178     default ValueRange range(TemporalField field) {
179         return TemporalAccessor.super.range(field);
180     }
181 
182     /**
183      * Gets the value of the specified field from this era as an {@code int}.
184      * <p>
185      * This queries this era for the value for the specified field.
186      * The returned value will always be within the valid range of values for the field.
187      * If it is not possible to return the value, because the field is not supported
188      * or for some other reason, an exception is thrown.
189      * <p>
190      * If the field is a {@link ChronoField} then the query is implemented here.
191      * The {@code ERA} field returns the value of the era.
192      * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
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. Whether the value can be obtained,
197      * and what the value represents, is determined by the field.
198      *
199      * @param field  the field to get, not null
200      * @return the value for the field
201      * @throws DateTimeException if a value for the field cannot be obtained or
202      *         the value is outside the range of valid values for the field
203      * @throws UnsupportedTemporalTypeException if the field is not supported or
204      *         the range of values exceeds an {@code int}
205      * @throws ArithmeticException if numeric overflow occurs
206      */
207     @Override  // override for Javadoc and performance
208     default int get(TemporalField field) {
209         if (field == ERA) {
210             return getValue();
211         }
212         return TemporalAccessor.super.get(field);
213     }
214 
215     /**
216      * Gets the value of the specified field from this era as a {@code long}.
217      * <p>
218      * This queries this era for the value for the specified field.
219      * If it is not possible to return the value, because the field is not supported
220      * or for some other reason, an exception is thrown.
221      * <p>
222      * If the field is a {@link ChronoField} then the query is implemented here.
223      * The {@code ERA} field returns the value of the era.
224      * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}.
225      * <p>
226      * If the field is not a {@code ChronoField}, then the result of this method
227      * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)}
228      * passing {@code this} as the argument. Whether the value can be obtained,
229      * and what the value represents, is determined by the field.
230      *
231      * @param field  the field to get, not null
232      * @return the value for the field
233      * @throws DateTimeException if a value for the field cannot be obtained
234      * @throws UnsupportedTemporalTypeException if the field is not supported
235      * @throws ArithmeticException if numeric overflow occurs
236      */
237     @Override
238     default long getLong(TemporalField field) {
239         if (field == ERA) {
240             return getValue();
241         } else if (field instanceof ChronoField) {
242             throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
243         }
244         return field.getFrom(this);
245     }
246 
247     //-----------------------------------------------------------------------
248     /**
249      * Queries this era using the specified query.
250      * <p>
251      * This queries this era using the specified query strategy object.
252      * The {@code TemporalQuery} object defines the logic to be used to
253      * obtain the result. Read the documentation of the query to understand
254      * what the result of this method will be.
255      * <p>
256      * The result of this method is obtained by invoking the
257      * {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
258      * specified query passing {@code this} as the argument.
259      *
260      * @param <R> the type of the result
261      * @param query  the query to invoke, not null
262      * @return the query result, null may be returned (defined by the query)
263      * @throws DateTimeException if unable to query (defined by the query)
264      * @throws ArithmeticException if numeric overflow occurs (defined by the query)
265      */
266     @SuppressWarnings("unchecked")
267     @Override
268     default <R> R query(TemporalQuery<R> query) {
269         if (query == TemporalQueries.precision()) {
270             return (R) ERAS;
271         }
272         return TemporalAccessor.super.query(query);
273     }
274 
275     /**
276      * Adjusts the specified temporal object to have the same era as this object.
277      * <p>
278      * This returns a temporal object of the same observable type as the input
279      * with the era changed to be the same as this.
280      * <p>
281      * The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
282      * passing {@link ChronoField#ERA} as the field.
283      * <p>
284      * In most cases, it is clearer to reverse the calling pattern by using
285      * {@link Temporal#with(TemporalAdjuster)}:
286      * <pre>
287      *   // these two lines are equivalent, but the second approach is recommended
288      *   temporal = thisEra.adjustInto(temporal);
289      *   temporal = temporal.with(thisEra);
290      * </pre>
291      * <p>
292      * This instance is immutable and unaffected by this method call.
293      *
294      * @param temporal  the target object to be adjusted, not null
295      * @return the adjusted object, not null
296      * @throws DateTimeException if unable to make the adjustment
297      * @throws ArithmeticException if numeric overflow occurs
298      */
299     @Override
300     default Temporal adjustInto(Temporal temporal) {
301         return temporal.with(ERA, getValue());
302     }
303 
304     //-----------------------------------------------------------------------
305     /**
306      * Gets the textual representation of this era.
307      * <p>
308      * This returns the textual name used to identify the era,
309      * suitable for presentation to the user.
310      * The parameters control the style of the returned text and the locale.
311      * <p>
312      * If no textual mapping is found then the {@link #getValue() numeric value} is returned.
313      * <p>
314      * This default implementation is suitable for all implementations.
315      *
316      * @param style  the style of the text required, not null
317      * @param locale  the locale to use, not null
318      * @return the text value of the era, not null
319      */
320     default String getDisplayName(TextStyle style, Locale locale) {
321         return new DateTimeFormatterBuilder().appendText(ERA, style).toFormatter(locale).format(this);
322     }
323 
324     // NOTE: methods to convert year-of-era/proleptic-year cannot be here as they may depend on month/day (Japanese)
325 }