TreeMap.putAll 给出的键超出范围

Question

In my code,

            SortedMap<Integer, Data> subMap;

            subMap = (db.getDataMap()).tailMap(previousServer);

            SortedMap<Integer, Data>  temp = (db.getDataMap()).headMap(presentServer);
            //System.out.println(subMap);
            //System.out.println(temp);
            subMap.putAll(temp);

suppose tailMap() returns nothing, so subMap is an empty Map, but temp has few key-value pair. So adding temp to subMap via subMap.putAll(temp) is giving me "key out of range". But if i do temp.putAll(subMap) then everything works fine.

What could be the reason here?

Answer 1

SEE http://docs.oracle.com/javase/7/docs/api/java/util/SortedMap.html#tailMap(K)

Note : several methods return submaps with restricted key ranges. Such ranges are half-open, that is, they include their low endpoint but not their high endpoint (where applicable). If you need a closed range (which includes both endpoints), and the key type allows for calculation of the successor of a given key, merely request the subrange from lowEndpoint to successor(highEndpoint). For example, suppose that m is a map whose keys are strings. The following idiom obtains a view containing all of the key-value mappings in m whose keys are between low and high, inclusive:

SortedMap<String, V> sub = m.subMap(low, high+"\0");

A similar technique can be used to generate an open range (which contains neither endpoint). The following idiom obtains a view containing all of the key-value mappings in m whose keys are between low and high, exclusive:

SortedMap<String, V> sub = m.subMap(low+"\0", high);

Answer 2

来自文档的状态

IllegalArgumentException if fromKey is greater than toKey; or if this map itself has a restricted range, and fromKey or toKey lies outside the bounds of the range

Answer 3

I found this problem very awkward, as only soln I could find was to replace code in a function f() returning SortedMap:

return docmap.headMap(nextkey);

where the returned map has a 'restricted range' (but there is no easy way to test this via a call that would be nice to have like map.isRangeRestricted())

with code that copy constructs a new map based on the restricted-range map:

return new TreeMap(docmap.headMap(nextkey))

Otherwise the client code, which is making a call such as

mmap.putAll(f()), where mmap is non-empty (and in this case also has a restricted range as earlier output from f() also), barfs.

I also find it counterintuitive that mmap can apparently have a restricted range but not mind doing a putAll as long as the map whose contents are being added does not have a restricted range as well.