Summary
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In order to accommodate the future addition of JapaneseEra without spec changes, loosening the current JapaneseEra spec would be desired.
Problem
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The current spec does not mention available eras returned from of()/valueOf()/values() methods, especially it is unclear if a new era is declared by the Japanese government. This would be more problematic for the maintenance releases.
Solution
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Specify the possible values returned from those static methods, and their parameters.
Specification
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Add the following sentence in the class description:
* The number of the valid eras may increase, as new eras may be
* defined by the Japanese government. Once an era is defined,
* subsequent versions of this class will add a singleton instance
* for it. The defined era is expected to have a consecutive integer
* associated with it.
Add the following paragraph to of(int) method description:
* <p>
* In addition to the known era singletons, values for additional
* eras may be defined. Those values are the {@link Era#getValue()}
* of corresponding eras from the {@link #values()} method.
Add the following paragraph to valueOf(String) method description:
* <p>
* Valid era names are the names of eras returned from {@link #values()}.
Change the first paragraph of values() method from:
* Returns an array of JapaneseEras.
to:
* Returns an array of JapaneseEras. The array may contain eras defined
* by the Japanese government beyond the known era singletons.