Java 8可选asSet（） [英] Java 8 Optional asSet()

问题描述

所以我一直在使用Guava的Optional一段时间了，我转到Java 8所以我想使用它的Optional类，但它没有我最喜欢的方法来自Guava，asSet（）。有没有办法用Java 8 Optional来做到这一点，我没有看到。我喜欢能够将可选项视为一个集合，所以我可以这样做：

So I have been using Guava's Optional for a while now, and I moving to Java 8 so I wanted to use it's Optional class, but it doesn't have my favorite method from Guava, asSet(). Is there a way to do this with the Java 8 Optional that I am not seeing. I love being able to treat optional as a collection so I can do this:

for( final User u : getUserOptional().asSet() ) {
   return u.isPermitted(getPermissionRequired());
}

在某些情况下，无需额外的变量。

In some cases avoids the need for an additional variable.

IE

 Optional<User> optUser = getUserOptional();
 if ( optUser.isPresent() ) {
     return optUser.get().isPermitted(getPermissionRequired());
 }

是否有一种简单的方法可以在Java 8的Optional中复制Guava样式？

Is there an easy way to replicate the Guava style in Java 8's Optional?

谢谢

推荐答案

有一种转换<$的简单方法c $ c>可选到集合。它就像可选的任何其他转换一样：

There is a simple way of converting an Optional into a Set. It works just like any other conversion of an Optional:

给定可选< T> ; o 你可以调用

o.map(Collections::singleton).orElse(Collections.emptySet())

获得设置< T> 。如果您不喜欢在每种情况下调用 Collections.emptySet（）的想法，您可以将其转换为惰性评估：

to get a Set<T>. If you don’t like the idea of Collections.emptySet() being called in every case you can turn it into a lazy evaluation:

o.map(Collections::singleton).orElseGet(Collections::emptySet)

然而，这种方法太过微不足道，无法产生性能差异。所以这只是编码风格的问题。

however, the method is too trivial to make a performance difference. So it’s just a matter of coding style.

你也可以用它来按预期迭代：

You can also use it to iterate like intended:

for(T t: o.map(Collections::singleton).orElse(Collections.emptySet()))
    // do something with t, may include a return statement

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