Asking about the interesting behaviours of TreeMap.putAll

[David Holmes]

HI Charles,

I tend to agree with you. In this case, in my opinion, 
AbstractMap.putAll has no business saying that it is equivalent to 
calling put() as that should be part of the implementation note, not the 
actual spec. Subclasses should be free to implement putAll in the most 
efficient manner possible as TreeMap does.

David

On 2/03/2012 6:17 PM, Charles Lee wrote:
> Hi guys,
>
> I have a small test case[1] and the two invokes of putAll have different
> behaviors: the first invocation does not use the override put but the
> second invocation does.
> The root cause about this can be find in the TreeMap code:
>
> /if (size==0 && mapSize!=0 && map instanceof SortedMap) {
> Comparator c = ((SortedMap)map).comparator();
> if (c == comparator || (c != null && c.equals(comparator))) {
> ++modCount;
> try {
> buildFromSorted(mapSize, map.entrySet().iterator(),
> null, null);
> } catch (java.io.IOException cannotHappen) {
> } catch (ClassNotFoundException cannotHappen) {
> }
> return;
> }
> }/
>
> When meet some situations, buildFromSorted will be invoked instead of
> put. I understand it is a speed up, but it may confuse people: "I need
> my own put because of something, but interestingly sometimes it will not
> be called when putAll and I do not find the reason from the api spec."
>
>  From the api spec of TreeMap's putAll, it says nothing about put. But
> from the api spec of AbstractMap's putAll and Map's putAll, they said:
> / "The effect of this call is equivalent to that of calling put(k, v) on
> this map once for each mapping from key k to value v in the specified
> map. "
> /The spec clearly say that, putAll will use put, that means, we can not
> use a putAll in an override put. Otherwise, it will recursive endlessly.
> So can I use a putAll in the override put method in an class which
> extends the TreeMap?
>
> [1]
> public class TreeMapTest<K, V> extends TreeMap<K, V> {
> @Override
> public V put(K key, V value) {
> System.out.println(key + " : " + value);
> return super.put(key, value);
> }
>
> /**
> * @param args
> */
> public static void main(String[] args) {
> TreeMapTest<Integer, Integer> mTreeMap = new TreeMapTest<>();
> TreeMap<Integer, Integer> mt = new TreeMap<>();
> mt.put(1, 1);
> mTreeMap.putAll(mt);
>
> mTreeMap.clear();
> mTreeMap.put(2, 2);
> mTreeMap.putAll(mt);
> }
> }
>