List.addAll throwing UnsupportedOperationException

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Java List.add() UnsupportedOperationException (7 answers)

Closed 8 months ago.

List.addAll throwing UnsupportedOperationException when trying to add another list.

List<String> supportedTypes = Arrays.asList("6500", "7600"};

and in loop I am doing,

supportedTypes.addAll(Arrays.asList(supportTypes.split(","))); //line 2

reading supportTypes from a file.

But line 2 throws a UnsupportedOperationException, but I am not able to determine why?

I am adding another list to a list, then why this operation is unsupported?

Answer 1

Problem is that Arrays.asList method returns instance of java.util.Arrays.ArrayList which doesn't support add/remove operations on elements. It's not surprizing that addAll method throws exception because add method for java.util.Arrays.ArrayList is defined as:

public void add(int index, E element) {
    throw new UnsupportedOperationException();
}

Related question:

Arrays.asList() Confusing source code

From the documentation:

Arrays.asList returns a fixed-size list backed by the specified array.

Answer 2

In my case this exception occured when I called adapter.addAll(items), where adapter was a custom ArrayAdapter. This CustomAdapter had a parameter of type Array instead of ArrayList.

Answer 3

This error also happens when the list is initialized with Collections.emptyList(), which is immutable:

List<String> myList = Collections.emptyList();

Instead, initialize it with a mutable list. For example

List<String> myList = new ArrayList<>();

Answer 4

Arrays.asList returns a fixed-size list.

If you to want be able to add elements to the list, do:

List<String> supportedTypes = new ArrayList<>(Arrays.asList("6500", "7600"});
supportedTypes.addAll(Arrays.asList(supportTypes.split(",")));

Answer 5

Arrays.asList returns a fixed sized list backed by an array, and you can't add elements to it.

You can create a modifiable list to make addAll work :

List<String> supportedTypes = new ArrayList<String>(Arrays.asList("6500", "7600", "8700"));