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Java: set-size List issue UnsupportedOperationException thrown

Answer 1

A:

List is an interface. It (like Collection) defines optional operations. Optional operations are part of the interface (for consistency) but there is no guarantee that subtypes would actually support them (it kind of violates behavioral subtyping). In other words, not all actual implementations of lists have to support these operations, they just have to document whether they do.

What actual list type are you using? ArrayList? LinkedList? A custom type?

For the best of my knowledge ArrayList DOES support the set operation. I am not sure about LinkedList If you have a custom implementation, it may not support it unless you override the method.

Uri 2010-04-30 16:23:47

should not be rather a comment than answer?

Gabriel Ščerbák 2010-04-30 16:25:15

@Gabirle: I was in the process of editing it into an answer.

Uri 2010-04-30 16:26:14

Answer 2

A:

List is not a class, it is just an interface. Are you implementing your own List? Or using a predefined one?

If it is some 3rd part library implementation of List, maybe that operation is simply not supported by that implementation (hence the exception).

Lars Andren 2010-04-30 16:24:56

Answer 3

+2 A:

You can see it from your stacktrace, the List used is a polyglot.util.TypedList, which can be constructed immutable.

set calls tryIns, which checks if the list is immutable (see source):

private  final void tryIns(Collection coll) {
  if (immutable)
    throw new UnsupportedOperationException JavaDoc(
                    "Add to an immutable TypedListIterator");

As you already found out set is an optional operation and this implementation of this List does not allow changes (if constructed immutable).

Peter Lang 2010-04-30 16:41:48

My problem was fixed by creating a new TypedList and inserting all the elements from the old list into the new one along with the new elements that I wanted to add to the list or change.

tuckster 2010-05-01 19:11:08

Answer 4

A:

Here are some suggestions for fixes

If your code creates the original list, then change the constructor call so that it is mutable.
Otherwise, if the code in ITypeChecker.enter() allows you to replace the list reference you can create a mutable list and use that,

e.g.

List immutable = ....; // your immutable list
List mutable = new LinkedList(immutable);
// pass `mutable` to the rest of your code so the new list is used

mdma 2010-04-30 19:59:25

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Java: set-size List issue UnsupportedOperationException thrown

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