Java:EnumSet.copyOf-是否有改进的空间? [英] Java: EnumSet.copyOf -- is there a room for improvement?
问题描述
我需要创建一个 EnumSet 从一组.我决定使用 EnumSet#copyOf 方法.但是，由于此方法的局限性:
I need to create an EnumSet from a Set. I decided to use the EnumSet#copyOf method. However, because of a restriction on this method:
the specified collection must contain at least one element (in order to determine the new enum set's element type)
我需要确保集合不为空.然后，代码变为:
I need to ensure that the collection is not empty. The code then becomes:
enum Color {RED, GREEN, BLUE};
Set<Color> set = ... // get it from somewhere
if (set.isEmpty()) {
return EnumSet.noneOf(Color.class);
else
return EnumSet.copyOf(set);
enum Color {RED, GREEN, BLUE};
Set<Color> set = ... // get it from somewhere
if (set.isEmpty()) {
return EnumSet.noneOf(Color.class);
else
return EnumSet.copyOf(set);
也许对javac而言，确定传递给copyOf方法的集合的成员的正确类型确实存在局限性，但我无法克服这样的感觉，我不得不依靠上述方法来满足空集合.然后是我的问题:
Perhaps there is a real limitation on javac to determine the correct type of members of the collection passed to copyOf method, but I can't get over the feeling that I have to resort to something like above to cater for the empty collection. Here are my questions then:
-
究竟在这里不能接受空集合的局限性是什么?
Exactly what is the limitation that the empty collection can't be accepted here?
像copyOf(Collection<Enum<E>>)这样的方法签名是否可以解决此问题?
Would a method signature like copyOf(Collection<Enum<E>>) have solved this problem?
如果是，还会带来什么其他问题?
If yes, what other problems would it have created?
推荐答案
根据 EnumSet.copyOf空集合会引发IllegalArgumentException ，似乎有用的是接受构造函数的复制构造函数，这在创建新的EnumSet时是必需的:
In light of EnumSet.copyOf empty collection throws IllegalArgumentException, what would seem to be of use would be a copy constructor which accepted an element type parameter, as is necessary when creating a new EnumSet:
EnumSet(Class<E>elementType, Enum<?>[] universe)
public static <E extends Enum<E>> EnumSet<E> copyOf(Collection<E> c, Class<E> elementType);
虽然节省的成本很小，但清晰度却是可观的.对比:
While the savings are small, the gain in clarity is significant. Contrast:
if ( set.isEmpty() )
return EnumSet.noneOf(Color.class);
else
return EnumSet.copyOf(set);
return EnumSet.copyOf(set, Color.class);
意图只是将给定集合复制为EnumSet.简单，直接地表达这种意图似乎是最合适的.
The intent is simply to copy a given set as an EnumSet. A simple, direct, expression of that intent seems most appropriate.
这篇关于Java:EnumSet.copyOf-是否有改进的空间?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
