Integer class is a wrapper for int. If it is not marked final, then any
other class can extend it and modify the behavior of Integer
operations. To avoid this Integer wrapper class is marked as final.
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class ApiClass {
private final List<Integer> intList;
ApiClass (List<Integer> ints) {
// Make a defensive copy
intList = new ArrayList<Integer>(ints);
// Go through the list, and check the values
}
}