java – Collections.unmodifiable* how to define?


It is known that there is a java.util.Collections class that has methods of the unmodifiable* type that return immutable collections. Now the question is how to determine that a collection is immutable?


You will hardly find any universal good solution.

In my opinion, the least crutch is .getClass().isInstance(...) :

List<String> list = new ArrayList<>();
List<String> unmodifiableList = Collections.unmodifiableList(list);
boolean isUnmodifiable = Collections.unmodifiableList(list).getClass().isInstance(unmodifiableList);

More options:

  1. Catch UnsupportedOperationException when adding an element. But then, in the case of a mutable collection, the element must be removed after the test.
  2. .getClass().getSimpleName().equals(...) .
Scroll to Top