List.addAll throwing UnsupportedOperationException when trying to add another list [duplicate]

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.