Java 将集合转换为列表
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Convert Collection to List
提问by Mercer
I would like to ask: how do you convert a Collectionto a Listin Java?
请问：在Java中如何将a转换Collection为a List？
采纳答案by Uri
If you have already created an instance of your List subtype (e.g., ArrayList, LinkedList), you could use the addAll method.
如果您已经创建了 List 子类型的实例（例如，ArrayList、LinkedList），则可以使用 addAll 方法。
e.g.,
例如，
l.addAll(myCollection)
Many list subtypes can also take the source collection in their constructor.
许多列表子类型也可以在其构造函数中使用源集合。
回答by Michael Myers
Collection<MyObjectType> myCollection = ...;
List<MyObjectType> list = new ArrayList<MyObjectType>(myCollection);
See the Collections trailin the Java tutorials.
回答by bmargulies
Make a new list, and call addAllwith the Collection.
创建一个新列表，并addAll使用 Collection调用。
回答by Cshah
you can use either of the 2 solutions .. but think about whether it is necessary to clone your collections, since both the collections will contain the same object references
您可以使用这两种解决方案中的任何一种..但请考虑是否有必要克隆您的集合，因为这两个集合都将包含相同的对象引用
回答by Omnipresent
Collectionand Listare interfaces. You can take any Implementation of the Listinterface: ArrayList LinkedListand just cast it back to a Collectionbecause it is at the Top
Collection并且List是接口。您可以采用List接口的任何实现：ArrayList LinkedList并将其强制转换回 aCollection因为它位于顶部
Example below shows casting from ArrayList
下面的示例显示了从 ArrayList
public static void main (String args[]) {
Collection c = getCollection();
List myList = (ArrayList) c;
}
public static Collection getCollection()
{
Collection c = new ArrayList();
c.add("Apple");
c.add("Oranges");
return c;
}
回答by Sandeep Bhardwaj
List list;
if (collection instanceof List)
{
list = (List)collection;
}
else
{
list = new ArrayList(collection);
}
回答by Vijay Kumar Rajput
Thanks for Sandeep putting it- Just added a null check to avoid NullPointerException in else statement.
感谢 Sandeep 把它 - 刚刚添加了一个空检查以避免在 else 语句中出现 NullPointerException。
if(collection==null){
return Collections.emptyList();
}
List list;
if (collection instanceof List){
list = (List)collection;
}else{
list = new ArrayList(collection);
}
