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

Question

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

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

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

Answer 1

• Collections.EMPTY_LIST returns an old-style List
• Collections.emptyList() uses type-inference and therefore returns List<T>

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.

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

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

Answer 2

Lets get to the source :

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

and

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

Answer 3

They are absolutely equal objects.

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.

Answer 4

In other words, EMPTY_LIST is not type safe:

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

As compared to:

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