java 用于将对象包装在集合中的实用方法
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Utility method for wrapping an object in a collection
提问by Tom Hawtin - tackline
I'm looking for a static method in the Java core libraries or some other commonly used dependency — preferably one of Apache — that does the following:
我正在 Java 核心库或其他一些常用依赖项（最好是 Apache 之一）中寻找静态方法，它执行以下操作：
public static <T> Collection<T> wrap(final T object){
final Collection<T> collection = new ArrayList<T>();
collection.add(object);
return collection;
}
Do you know where such a method already exists? Since I guess the problem is common, I don't want to duplicate it's solution.
你知道哪里已经有这样的方法了吗？因为我猜这个问题很常见，所以我不想复制它的解决方案。
回答by Tom Hawtin - tackline
java.util.Collections.singleton(object)will give you an immutable Set. singletonListis also available.
java.util.Collections.singleton(object)会给你一个不变的Set。singletonList也可用。
Less efficiently java.util.Arrays.asList(object)will give you a mutable (can use list.set(0, x);), but non-structurally changeable (can't add or remove) List. It is a bit more expensive as there is an extra array that is created client-side.
效率较低java.util.Arrays.asList(object)会给你一个可变的（可以使用list.set(0, x);），但非结构可变的（不能添加或删除）List。它有点贵，因为有一个额外的数组是在客户端创建的。
回答by Sheepy
Here are some efficient ways to wrap Java object(s) in List, as of Java 8.
从 Java 8 开始，这里有一些在 List 中包装 Java 对象的有效方法。
Collections.singletonList: Single item, immutable, since 1.3. Collections.singletonList( object )
High performance backed by internal class.
收藏。singletonList：单个项目，不可变，自 1.3 起。Collections.singletonList( object )
内部类支持的高性能。
Collections.nCopies: One object, zeroto many items, immutable, since 1.2. Collections.nCopies( number_of_copy, object )
High performance backed by internal class. All items point to same object.
收藏。nCopies：一个对象，零到多个项目，不可变，自 1.2 起。Collections.nCopies( number_of_copy, object )
内部类支持的高性能。所有项目都指向同一个对象。
Array.asList: Any number of objects, sizeimmutable (individual elements mutable), since 1.2. Arrays.asList( object1, object2, object3 )
Backed by internal class. Items are converted to array at compile timeand this array directly backs the List.
大批。asList：任意数量的对象，大小不可变（单个元素可变），自 1.2 起。Arrays.asList( object1, object2, object3 )
由内部类支持。项目在编译时转换为数组，该数组直接支持列表。
new ArrayList(Collection): Any number of objects, mutable, since 1.2new ArrayList<>( Arrays.asList( object1, object2, object3 ) )
The ArrayList is created with an array cloneand an array copy, and so does not use any loops.
new ArrayList(Collection)：任意数量的对象，可变的，自 1.2 起new ArrayList<>( Arrays.asList( object1, object2, object3 ) )
ArrayList 是使用数组 clone和数组 copy 创建的，因此不使用任何循环。
回答by NimChimpsky
public static <E> ImmutableList<E> of(E element)
Returns an immutable list containing a single element. This list behaves and performs comparably to Collections.singleton(T), but will not accept a null element. It is preferable mainly for consistency and maintainability of your code.
返回包含单个元素的不可变列表。此列表的行为和性能与 Collections.singleton(T) 相当，但不接受空元素。主要是为了代码的一致性和可维护性。
回答by Martijn Courteaux
Don't be afraid of writing something yourself. As far as I know it doesn't exist. I think a reason for this is that the utility method decides which implementation of Collection it uses. In your case you chose for ArrayList, but there are a whole bunch of other collections.
不要害怕自己写一些东西。据我所知它不存在。我认为这样做的一个原因是实用程序方法决定了它使用的 Collection 实现。在您的情况下，您选择了 ArrayList，但还有一大堆其他集合。
回答by sharakan
java.util.Collections.singletonList() or singleton(). Note though that the result is immutable.
java.util.Collections.singletonList() 或 singleton()。请注意，结果是不可变的。
