Convert between EnumSet and array of boolean values

问题

I have an EnumSet and want to convert back-and-forth to/from an array of boolean primitives. If it works better, I could work with a List instead of an array, and/or Boolean objects rather than boolean primitives.

enum MyEnum { DOG, CAT, BIRD; }
EnumSet enumSet = EnumSet.of( MyEnum.DOG, MyEnum.CAT );

What I want to get on the other end is an array that looks like this:

[TRUE, TRUE, FALSE]

This Question here is similar to this one, Convert an EnumSet to an array of integers. Differences:

boolean or Boolean versus integers (obviously)
I want all members of the enum to be represented, with a TRUE for each enum element included in the EnumSet and a FALSE for each element that is excluded from the EnumSet. The other Question’s array includes only the items found in the EnumSet. (more importantly)

回答1:

To do that you'd basically write

MyEnum[] values = MyEnum.values(); // or MyEnum.class.getEnumConstants()
boolean[] present = new boolean[values.length];
for (int i = 0; i < values.length; i++) {
  present[i] = enumSet.contains(values[i]);
}

Going the other direction, from boolean array present created above to enumSet_ created below.

EnumSet<MyEnum> enumSet_ = EnumSet.noneOf ( MyEnum.class );  // Instantiate an empty EnumSet.
MyEnum[] values_ = MyEnum.values ();
for ( int i = 0 ; i < values_.length ; i ++ ) {
    if ( present[ i ] ) {  // If the array element is TRUE, add the matching MyEnum item to the EnumSet. If FALSE, do nothing, effectively omitting the matching MyEnum item from the EnumSet.
        enumSet_.add ( values_[ i ] );
    }
}

回答2:

For the present, I don't see a better solution than

Boolean[] b = Arrays.stream(MyEnum.values()).map(set::contains).toArray(Boolean[]::new);

To get an EnumSet from an array of boolean primitives by using zip

MyEnum[] enums = zip(Arrays.stream(MyEnum.values()), Arrays.stream(b),
    (e, b) -> b ? e : null).filter(Objects::nonNull).toArray(MyEnum[]::new);

回答3:

In Java 8 you could do it like this

List<Boolean> present = Arrays.stream(MyEnum.values()).map(enumSet::contains).collect(Collectors.toList());

To go the other way around you could do something like this

IntStream.range(0, present.size()).filter(present::get).mapToObj(i -> MyEnum.values()[i]).
    collect(Collectors.toCollection(() -> EnumSet.noneOf(MyEnum.class)));

来源：https://stackoverflow.com/questions/38366382/convert-between-enumset-and-array-of-boolean-values

标签

java

list

enums

boolean

enumset