Collections: EnumSet is a bit-vector set for enums

EnumSet stores enum constants as bits, making it far smaller and faster than HashSet, and it always iterates in declaration order.

Code

enum Day { MON, TUE, WED, THU, FRI, SAT, SUN }

var weekend = EnumSet.of(Day.SAT, Day.SUN);
var weekdays = EnumSet.complementOf(weekend);
var midweek = EnumSet.range(Day.TUE, Day.THU);

System.out.println("weekend  = " + weekend);
System.out.println("weekdays = " + weekdays);
System.out.println("midweek  = " + midweek);
System.out.println("all      = " + EnumSet.allOf(Day.class));

Output

weekend  = [SAT, SUN]
weekdays = [MON, TUE, WED, THU, FRI]
midweek  = [TUE, WED, THU]
all      = [MON, TUE, WED, THU, FRI, SAT, SUN]

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Published 2026-07-30