Method to extract all keys from LinkedHashMap into a List

Question

I am working with many LinkedHashMap that are either LinkedHashMap, LinkedHashMap or Linke

Answer 1

LinkedHashMap's consistent ordering applies to keys, values and entries.

You should be just fine doing:

ArrayList keys = new ArrayList<>(target.keySet());

If you need more assurance, take a look at the source code for LinkedHashMap. The important part:

private class KeyIterator extends LinkedHashIterator {
    public K next() { return nextEntry().getKey(); }
}

private class ValueIterator extends LinkedHashIterator {
    public V next() { return nextEntry().value; }
}

private class EntryIterator extends LinkedHashIterator> {
    public Map.Entry next() { return nextEntry(); }
}

// These Overrides alter the behavior of superclass view iterator() methods
Iterator newKeyIterator()   { return new KeyIterator();   }
Iterator newValueIterator() { return new ValueIterator(); }
Iterator> newEntryIterator() { return new EntryIterator(); }

So the iterators for the keys, values and entries all come from the same source (nextEntry()) which uses the linked list for iteration order.