* Most calendar systems have a single epoch dividing the time-line into two eras. * However, some calendar systems, have multiple eras, such as one for the reign * of each leader. * In all cases, the era is conceptually the largest division of the time-line. * Each chronology defines the Era's that are known Eras and a * {@link Chronology#eras Chronology.eras} to get the valid eras. *
* For example, the Thai Buddhist calendar system divides time into two eras, * before and after a single date. By contrast, the Japanese calendar system * has one era for the reign of each Emperor. *
* Instances of {@code Era} may be compared using the {@code ==} operator. *
* This interface must be implemented with care to ensure other classes operate correctly. * All implementations must be singletons - final, immutable and thread-safe. * It is recommended to use an enum whenever possible. */ public interface Era extends TemporalAccessor, TemporalAdjuster { /** * Gets the numeric value associated with the era as defined by the chronology. * Each chronology defines the predefined Eras and methods to list the Eras * of the chronology. *
* All fields, including eras, have an associated numeric value. * The meaning of the numeric value for era is determined by the chronology * according to these principles: *
* This checks if this era can be queried for the specified field. * If false, then calling the {@link #range(TemporalField) range} and * {@link #get(TemporalField) get} methods will throw an exception. *
* If the field is a {@link ChronoField} then the query is implemented here. * The {@code ERA} field returns true. * All other {@code ChronoField} instances will return false. *
* If the field is not a {@code ChronoField}, then the result of this method * is obtained by invoking {@code TemporalField.isSupportedBy(TemporalAccessor)} * passing {@code this} as the argument. * Whether the field is supported is determined by the field. * * @param field the field to check, null returns false * @return true if the field is supported on this era, false if not */ @Override boolean isSupported(@Nullable TemporalField field); /** * Gets the range of valid values for the specified field. *
* The range object expresses the minimum and maximum valid values for a field. * This era is used to enhance the accuracy of the returned range. * If it is not possible to return the range, because the field is not supported * or for some other reason, an exception is thrown. *
* If the field is a {@link ChronoField} then the query is implemented here. * The {@code ERA} field returns the range. * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}. *
* If the field is not a {@code ChronoField}, then the result of this method * is obtained by invoking {@code TemporalField.rangeRefinedBy(TemporalAccessor)} * passing {@code this} as the argument. * Whether the range can be obtained is determined by the field. *
* The default implementation must return a range for {@code ERA} from * zero to one, suitable for two era calendar systems such as ISO. * * @param field the field to query the range for, not null * @return the range of valid values for the field, not null * @throws DateTimeException if the range for the field cannot be obtained * @throws UnsupportedTemporalTypeException if the unit is not supported */ @Override // override for Javadoc ValueRange range(TemporalField field); /** * Gets the value of the specified field from this era as an {@code int}. *
* This queries this era for the value of the specified field. * The returned value will always be within the valid range of values for the field. * If it is not possible to return the value, because the field is not supported * or for some other reason, an exception is thrown. *
* If the field is a {@link ChronoField} then the query is implemented here. * The {@code ERA} field returns the value of the era. * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}. *
* If the field is not a {@code ChronoField}, then the result of this method * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)} * passing {@code this} as the argument. Whether the value can be obtained, * and what the value represents, is determined by the field. * * @param field the field to get, not null * @return the value for the field * @throws DateTimeException if a value for the field cannot be obtained or * the value is outside the range of valid values for the field * @throws UnsupportedTemporalTypeException if the field is not supported or * the range of values exceeds an {@code int} * */ @Override // override for Javadoc and performance int get(TemporalField field); /** * Gets the value of the specified field from this era as a {@code long}. *
* This queries this era for the value of the specified field. * If it is not possible to return the value, because the field is not supported * or for some other reason, an exception is thrown. *
* If the field is a {@link ChronoField} then the query is implemented here. * The {@code ERA} field returns the value of the era. * All other {@code ChronoField} instances will throw an {@code UnsupportedTemporalTypeException}. *
* If the field is not a {@code ChronoField}, then the result of this method * is obtained by invoking {@code TemporalField.getFrom(TemporalAccessor)} * passing {@code this} as the argument. Whether the value can be obtained, * and what the value represents, is determined by the field. * * @param field the field to get, not null * @return the value for the field * @throws DateTimeException if a value for the field cannot be obtained * @throws UnsupportedTemporalTypeException if the field is not supported * */ @Override long getLong(TemporalField field); //----------------------------------------------------------------------- /** * Adjusts the specified temporal object to have the same era as this object. *
* This returns a temporal object of the same observable type as the input * with the era changed to be the same as this. *
* The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)} * passing {@link ChronoField#ERA} as the field. *
* In most cases, it is clearer to reverse the calling pattern by using * {@link Temporal#with(TemporalAdjuster)}: *
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisEra.adjustInto(temporal);
* temporal = temporal.with(thisEra);
*
* * This instance is immutable and unaffected by this method call. * * @param temporal the target object to be adjusted, not null * @return the adjusted object, not null * @throws DateTimeException if unable to make the adjustment * */ @Override Temporal adjustInto(Temporal temporal); //----------------------------------------------------------------------- // /** // * Gets the textual representation of this era. // *
// * This returns the textual name used to identify the era, // * suitable for presentation to the user. // * The parameters control the style of the returned text and the locale. // *
// * If no textual mapping is found then the {@link #getValue() numeric value} is returned. // * // * @apiNote This default implementation is suitable for most implementations. // * // * @param style the style of the text required, not null // * @param locale the locale to use, not null // * @return the text value of the era, not null // */ // default String getDisplayName(TextStyle style, Locale locale) { // return new DateTimeFormatterBuilder().appendText(ERA, style).toFormatter(locale).format(this); // } // NOTE: methods to convert year-of-era/proleptic-year cannot be here as they may depend on month/day (Japanese) }