Asking about the interesting behaviours of TreeMap.putAll

[Charles Lee]

Hi David,

I also notice that in the AbstractMap doc, it also says:
"The documentation for each non-abstract method in this class describes 
its implementation in detail. Each of these methods may be overridden if 
the map being implemented admits a more efficient implementation. "

If this is the logic[1], shall we add some implementation notes in the 
subclass of AbstractMap when some default behaviours have been changed? 
 From the spec, the only implementation of putAll I can find from the 
TreeMap is using the put method.

[1] The logic means:
a. We have to place the implementation note in every specified method api
b. The subclass feels free to change the implementation.

On 03/02/2012 05:02 PM, David Holmes wrote:
> 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);
>> }
>> }
>>
>


-- 
Yours Charles