An era in the ISO calendar system.

The ISO-8601 standard does not define eras. A definition has therefore been created with two eras - 'Current era' (CE) for years on or after 0001-01-01 (ISO), and 'Before current era' (BCE) for years before that.

ISO years and eras

year-of-era	era	proleptic-year
2	CE	2
1	CE	1
1	BCE	0
2	BCE	-1

Do not use ordinal() to obtain the numeric representation of IsoEra. Use getValue() instead.

extends Enum<IsoEra> implements Era

Since:  1.8

@implSpec This is an immutable and thread-safe enum.