Arrays in java violates ISP?

Question

The code below will throw UnsupportedOperationException in java :

String[] arr = {"a", "b", "c"};
List<String> list = Arrays.asList(arr);
list.add("d");

I'm a little confused isn't this an ISP violation ? Here class implements the List interface but can't implement its method add()

I thought that the solid principles are followed in most cases — LightSouls, Jun 26 '23 at 17:14
related: [Violation of single responsibility principle in Iterator from Java core](https://stackoverflow.com/q/33160222/1371329) — jaco0646, Jun 30 '23 at 18:43

score 4 · Answer 1 · answered Jun 26 '23 at 16:21

4

The List.add() method is defined as an optional operation:

boolean add(E e)

Appends the specified element to the end of this list (optional operation).

And further down it defines when it throws an UnsupportedOperationException:

Throws:

UnsupportedOperationException - if the add operation is not supported by this list

So the implementation (returned by Arrays.asList()) is doing what is "allowed" to do based on the specification of the java.util.List interface.

answered Jun 26 '23 at 16:21

Progman

16,827
6
33
48

Hm, if we can throw exception in any method we want, why then we need ISP ? – LightSouls Jun 26 '23 at 16:23
This answer explains how the `add()` method conforms to the _LSP_, but the _ISP_ has nothing to do with documentation. – jaco0646 Jun 30 '23 at 18:48

Joshua Fox · Accepted Answer · 2023-06-27T07:12:14.710

2

Yes, it does violate the Interface Segregation Principle, like any Unmodifiable collection. The designers of the Collections API could have created separate interfaces for write and read actions but decided to keep them together.

One could argue that this list does confirm to the ISP -- it has the add() function -- but the thing that it does with that function is not what you expect. [EDIT, per @progman below: And the exception can be considered part of the interface, because it is documented.]

Here is a related discussion on Software Engineering Stack Exchange.

edited Jun 27 '23 at 07:12

answered Jun 26 '23 at 16:19

Joshua Fox

18,704
23
87
147

Progman is conflating different principles. His argument is unrelated to the ISP. Your first paragraph is correct. – jaco0646 Jun 30 '23 at 18:55

Arrays in java violates ISP?

2 Answers2