Java 如何快速方便地创建一个单元素数组列表
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How to quickly and conveniently create a one element arraylist
提问by David T.
Is there a Utility method somewhere that can do this in 1 line? I can't find it anywhere in Collections, or List.
是否有可以在 1 行中执行此操作的实用程序方法？我在Collections, 或 中的任何地方都找不到它List。
public List<String> stringToOneElementList(String s) {
List<String> list = new ArrayList<String>();
list.add(s);
return list;
}
I don't want to re-invent the wheel unless I plan on putting fancy rims on it.
我不想重新发明轮子，除非我打算在上面装上花哨的轮辋。
Well... the type can be T, and not String. but you get the point. (with all the null checking, safety checks...etc)
嗯...类型可以是T，而不是String。但你明白了。（所有的空检查，安全检查......等）
采纳答案by Elliott Frisch
Fixed size List
固定尺寸 List
The easiest way, that I know of, is to create a fixed-size single element Listwith Arrays.asList(T...)like
据我所知，最简单的方法是创建一个固定大小的单个元素List，Arrays.asList(T...)例如
// Returns a List backed by a varargs T.
return Arrays.asList(s);
Variable size List
可变尺寸 List
If it needs vary in size you can construct an ArrayListand the fixed-sizeListlike
如果它需要不同的大小，您可以构建一个ArrayList和固定大小的List类似
return new ArrayList<String>(Arrays.asList(s));
and (in Java 7+) you can use the diamond operator <>to make it
并且（在 Java 7+ 中）您可以使用菱形运算符<>来制作它
return new ArrayList<>(Arrays.asList(s));
Single Element List
单元素列表
Collections can return a list with a single element with list being immutable:
集合可以返回一个包含单个元素的列表，列表是不可变的：
Collections.singletonList(s)
The benefit here is IDEs code analysis doesn't warn about single element asList(..) calls.
这里的好处是 IDE 代码分析不会警告单个元素 asList(..) 调用。
回答by SLaks
Very simply:
很简单：
Arrays.asList("Hi!")
回答by rgettman
You can use the utility method Arrays.asListand feed that result into a new ArrayList.
您可以使用实用程序方法Arrays.asList并将结果提供给新的ArrayList.
List<String> list = new ArrayList<String>(Arrays.asList(s));
Other options:
其他选项：
List<String> list = new ArrayList<String>(Collections.nCopies(1, s));
and
和
List<String> list = new ArrayList<String>(Collections.singletonList(s));
ArrayList(Collection)constructor.Arrays.asListmethod.Collections.nCopiesmethod.Collections.singletonListmethod.
With Java 7+, you may use the "diamond operator", replacing new ArrayList<String>(...)with new ArrayList<>(...).
在 Java 7+ 中，您可以使用“菱形运算符”，替换new ArrayList<String>(...)为new ArrayList<>(...).
Java 9
爪哇 9
If you're using Java 9+, you can use the List.ofmethod:
如果您使用的是 Java 9+，则可以使用以下List.of方法：
List<String> list = new ArrayList<>(List.of(s));
Regardless of the use of each option above, you may choose not to use the new ArrayList<>()wrapper if you don't need your list to be mutable.
不管上面的每个选项如何使用，new ArrayList<>()如果你不需要你的列表是可变的，你可以选择不使用包装器。
回答by user167019
The other answers all use Arrays.asList(), which returns an unmodifiable list (an UnsupportedOperationExceptionis thrown if you try to add or remove an element). To get a mutable list you can wrap the returned list in a new ArrayListas a couple of answers point out, but a cleaner solution is to use Guava'sLists.newArrayList()(available since at least Guava 10, released in 2011).
其他答案都使用Arrays.asList()，它返回一个不可修改的列表（UnsupportedOperationException如果您尝试添加或删除元素，则会抛出 an ）。要获得可变列表，您可以将返回的列表包装在一个 new 中，ArrayList正如几个答案所指出的那样，但更简洁的解决方案是使用Guava 的Lists.newArrayList()（至少从 2011 年发布的Guava 10 开始可用）。
For example:
例如：
Lists.newArrayList("Blargle!");
回答by Stein
Yet another alternative is double brace initialization, e.g.
另一种选择是双括号初始化，例如
new ArrayList<String>() {{ add(s); }};
but it is inefficient and obscure. Therefore only suitable:
但它是低效和晦涩的。因此只适合：
- in code that doesn't mind memory leaks, such as most unit tests and other short-lived programs;
- and if none of the other solutions apply, which I think implies you've scrolled all the way down here looking to populate a different type of container than the ArrayList in the question.
- 在不介意内存泄漏的代码中，例如大多数单元测试和其他短期程序；
- 如果其他解决方案都不适用，我认为这意味着您已经一直向下滚动，希望填充与问题中的 ArrayList 不同类型的容器。
回答by Andrew
Collections.singletonList(object)
the list created by this method is immutable.
此方法创建的列表是不可变的。
回答by Marko Jurisic
With Java 8 Streams:
使用 Java 8 流：
Stream.of(object).collect(Collectors.toList())
or if you need a set:
或者如果你需要一套：
Stream.of(object).collect(Collectors.toSet())
回答by vegemite4me
Seeing as Guava gets a mention, I thought I would also suggest Eclipse Collections(formerly known as GS Collections).
看到 Guava 被提及，我想我还建议使用Eclipse Collections（以前称为 GS Collections）。
The following examples all return a Listwith a single item.
以下示例都返回List带有单个项目的 a。
Lists.mutable.of("Just one item");
Lists.mutable.with("Or use with");
Lists.immutable.of("Maybe it must be immutable?");
Lists.immutable.with("And use with if you want");
There are similar methods for other collections.
其他集合也有类似的方法。
