Why does casting `toArray()` result to `String[]` cause a `ClassCastException`?

Unable to Convert toArray() Result to String[]

The following code consistently triggers a ClassCastException at line 3:

<code class="java">final String[] v1 = i18nCategory.translation.get(id);
final ArrayList<String> v2 = new ArrayList<>(Arrays.asList(v1));
String[] v3 = (String[])v2.toArray();</code>

This error persists regardless of whether v2 contains any elements or if its content exclusively comprises strings. What explains this behavior?

Resolution

toArray() returns an Object[], which cannot be directly cast to a String[] even if the elements in Object[] are strings. This is because generics are implemented at compile time only and are not present during runtime. As a result, toArray() cannot determine the intended array type.

To rectify this issue, use the following modified code:

<code class="java">String[] v3 = v2.toArray(new String[v2.size()]);</code>

This version creates an array of the correct type (String[]) with the appropriate length, eliminating the ClassCastException.

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