我没有找到这个具体问题的直接答案,所以......假设类:
class MyClass {
private final Set<String> tags;
MyClass(Set<String> initialTags) {
this.tags = ???(initialtags);
}
}
我只想要一个副本,而不关心集合的确切实现,以最小的开销,所以基本上是任何内部状态initialTags 的直接副本。我无法使用clone
,因为 Set 是接口(interface)。这可能吗,还是我必须使用类似 new HashSet<String>(tags);
的东西? ,需要决定类型吗?
假设:设置项目类型仅限于不可变。我可以相信调用者不会传递损坏的 initialTags
设置实现,我可以相信它对于此类中的任何内部使用都有足够好的性能。
我正在考虑尝试反射和clone(),但这看起来有点脏......
最佳答案
Guava 提供了一种方法:
/**
* Returns an immutable set containing the given elements, in order. Repeated
* occurrences of an element (according to {@link Object#equals}) after the
* first are ignored. This method iterates over {@code elements} at most once.
*
* <p>Note that if {@code s} is a {@code Set<String>}, then {@code
* ImmutableSet.copyOf(s)} returns an {@code ImmutableSet<String>} containing
* each of the strings in {@code s}, while {@code ImmutableSet.of(s)} returns
* a {@code ImmutableSet<Set<String>>} containing one element (the given set
* itself).
*
* <p>Despite the method name, this method attempts to avoid actually copying
* the data when it is safe to do so. The exact circumstances under which a
* copy will or will not be performed are undocumented and subject to change.
*
* @throws NullPointerException if any of {@code elements} is null
*/
public static <E> ImmutableSet<E> copyOf(Iterable<? extends E> elements) {
return (elements instanceof Collection)
? copyOf(Collections2.cast(elements))
: copyOf(elements.iterator());
}
关于java - 在构造函数中制作 Set<String> 的常规副本,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/13192474/