CollectionUtils.isEmpty（list）如何工作？

Question

List<String> list = null;  // line1
List<String> list = Collections.emptyList(); // line2

if(CollectionUtils.isEmpty(list)) {  // line3
   System.out.println("empty");  // line4
} else {
   list.forEach(value -> System.out.println(value));  // line5
}

If I initialize the list as per line2, why the if check prints the output as empty? But I change the check to list == null , it works fine. ie the code iterates on the empty list.

Answer 1

JavaDoc:

public static boolean isEmpty(Collection<?> coll)

Null-safe check if the specified collection is empty.

Null returns true.

Implemented:

return coll == null || coll.isEmpty();