java.util.Calendar.getDisplayName(int field, int style, Locale locale) returns era name in English instead of Japanese name. Below are the steps to reproduce the issue:-

Set JVM parameter java.locale.providers=CLDR

Calendar c = new Calendar.Builder()
            .setCalendarType("japanese")
            .setFields(ERA, 4, YEAR, 1, MONTH, MAY, DAY_OF_MONTH, 1)
            .build();

String eraName = c.getDisplayName(ERA, LONG, Locale.Japan);

Actual Result :- The value of eraName is "Heise"

Expected Result:- The value of eraName should be "平成"


Root Cause of issue:-

The cause of issue is that CLDR java resource file (FormatData_ja.java) generated by "CLDR Converter" does not contain required resource key "japanese.long.Eras". The "CLDR Converter" need to be fixed to address this issue.