如何解决这个JDK限制？

I'm looking for a class from the Java Collection Framework that would not allow null elements.

我正在寻找Java Collection Framework中不允许使用null元素的类。

Do you know one?

你知道吗？

7 个解决方案

#1

Most Queue implementations (with the notable exception of LinkedList) don't accept null.

大多数Queue实现（使用LinkedList的明显例外）不接受null。

EnumSet is a special-purpose Set implementation that doesn't allow null values.

EnumSet是一个特殊用途的Set实现，它不允许空值。

#2

Use Constraints:

使用约束：

import com.google.common.collect.Constraints;
...
Constraints.constrainedList(new ArrayList(), Constraints.notNull())

from Guava for maximum flexibility.

从番石榴获得最大的灵活性。

UPDATE: Guava Constraints has been deprecated in Release 15 - apparently without replacement.

更新：Guava约束已在第15版中弃用 - 显然没有替代。

UPDATE 2: As of now (Guava 19.0-rc2) Constrains is still there and not deprecated anymore. However, it's missing from the Javadoc.

更新2：截至目前（Guava 19.0-rc2）Constrains仍在那里，不再被弃用了。然而，它在Javadoc中缺失了。

I'm afraid that the Javadoc is right as MapConstraint have been deprecated in Release 19, too

我担心Javadoc是正确的，因为MapConstraint也在第19版中被弃用了

#3

There's a roundup of such collections here.

这里收集了这样的集合。

#4

Apache Commons Framework - CollectionUtils.addIgnoreNull

Adds to myList if myObj is not null.

如果myObj不为null，则添加到myList。

org.apache.commons.collections.CollectionUtils.addIgnoreNull(myList, myObj)

org.apache.commons.collections.CollectionUtils.addIgnoreNull（myList，myObj）

#5

Using Google Guava Predicates (the answer from @Joachim Sauer is deprecated)

使用Google Guava Predicates（@Joachim Sauer的答案已被弃用）

//list is the variable where we want to remove null elements
List nullRemovedList=Lists.newArrayList(Iterables.filter(list, Predicates.notNull()));

//Or convert to Immutable list
List nullRemovedList2=ImmutableList.copyOf(Iterables.filter(list, Predicates.notNull()));

#6

Hashtable does not allow null keys or values.

Hashtable不允许使用null键或值。

#7

Start here, the Collections API Page. Check out the "See Also" section. Follow the links. The decision to allow or disallow null is made by the implementing class; just follow the links in the various "See Also" sections to get to the implementing classes (for example, HashMap) then look at the insertion methods (generally a variation on add, push, or put) to see if that implementation permits null.

从这里开始，收集API页面。查看“另请参阅”部分。点击链接。允许或禁止null的决定由实施类决定;只需按照各种“另请参见”部分中的链接访问实现类（例如，HashMap），然后查看插入方法（通常是添加，推送或放置的变体），以查看该实现是否允许null。

#1