Hi.
On Fri, 4 Aug 2017 15:29:42 -0400, Simon Spero wrote:
On Aug 4, 2017 2:11 PM, "Gary Gregory" <[email protected]>
wrote:
For example, I have a enum like:
public enum CardinalDirection (NORTH,SOUTH,EAST,WEST)
public CardinalDirection nextRandomDirection() {
return rng.next(CardinalDirection.class);
}
This approach may be a bit slow if the random values are near an
inner
loop.
In order to select a random enum value, you need to get hold of an
array
containing all the possible values (equivalent to what gets returned
by the
generated "public static CardinalDirection[] values()".
This requires calling Class::getEnumConstants, which does a little
reflection, caches the result, then returns a clone of the resultant
array.
It may be better to construct a random enum value generator object
that
holds a copy of the values array, plus an RNG with the desired
characteristics.
A more general method would take an array of values, or a
Supplier<T[]>
function (e.g. CardinalDirection::values).
You could use a cache in the RNG, keyed by the class, but that's
still
going to be a bit expensive in the middle of a tight loop.
What about the following?
---CUT---
import org.apache.commons.rng.UniformRandomProvider;
import org.apache.commons.rng.simple.RandomSource;
public class RandomEnum<T extends Enum<T>> {
private final T[] values;
private final UniformRandomProvider rand =
RandomSource.create(RandomSource.SPLIT_MIX_64);
public RandomEnum(Class<T> c) {
values = c.getEnumConstants();
}
public T next() {
return values[rand.nextInt(values.length)];
}
}
---CUT---
Regards,
Gilles
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