Collections.emptyList（）和Collections.EMPTY_LIST之间有什么区别

In Java, we have Collections.emptyList() and Collections.EMPTY_LIST. Both have the same property:

在Java中，我们有Collections.emptyList（）和Collections.EMPTY_LIST。两者都具有相同的属性：

Returns the empty list (immutable). This list is serializable.

返回空列表（不可变）。此列表是可序列化的。

So what is the exact difference between using the one or the other?

那么使用这一个或另一个之间的确切区别是什么？

4 个解决方案

#1

Collections.EMPTY_LIST returns an old-style List
Collections.EMPTY_LIST返回旧式List
Collections.emptyList() uses type-inference and therefore returns List<T>
Collections.emptyList（）使用类型推断，因此返回List

Collections.emptyList() was added in Java 1.5 and it is probably always preferable. This way, you don't need to unnecessarily cast around within your code.

在Java 1.5中添加了Collections.emptyList（），它可能总是更可取。这样，您就不需要在代码中进行不必要的转换。

Collections.emptyList() intrinsically does the cast for you.

Collections.emptyList（）本质上为你做演员。

@SuppressWarnings("unchecked")
public static final <T> List<T> emptyList() {
    return (List<T>) EMPTY_LIST;
}

#2

Lets get to the source :

让我们来源：

 public static final List EMPTY_LIST = new EmptyList<>();

and

和

@SuppressWarnings("unchecked")
public static final <T> List<T> emptyList() {
    return (List<T>) EMPTY_LIST;
}

#3

They are absolutely equal objects.

它们绝对是平等的对象。

public static final List EMPTY_LIST = new EmptyList<>();

public static final <T> List<T> emptyList() {
    return (List<T>) EMPTY_LIST;
}

The only one is that emptyList() returns generic List<T>, so you can assign this list to generic collection without any warnings.

唯一的一个是emptyList（）返回通用List ，因此您可以将此列表分配给泛型集合，而不会发出任何警告。

#4

In other words, EMPTY_LIST is not type safe:

换句话说，EMPTY_LIST不是类型安全的：

  List list = Collections.EMPTY_LIST;
  Set set = Collections.EMPTY_SET;
  Map map = Collections.EMPTY_MAP;

As compared to:

相比于：

    List<String> s = Collections.emptyList();
    Set<Long> l = Collections.emptySet();
    Map<Date, String> d = Collections.emptyMap();

#1

Collections.EMPTY_LIST returns an old-style List
Collections.EMPTY_LIST返回旧式List
Collections.emptyList() uses type-inference and therefore returns List<T>
Collections.emptyList（）使用类型推断，因此返回List