Collections out of range

[shuba gopal]

The following code is an example in K & B. Why are # 5 and 6 "out of range"? # 5 is included in map but why the comment "out of range". why does #6 throw error?

TreeMap<String, String> map = new TreeMap<String, String>();
map.put("a", "ant"); map.put("d", "dog"); map.put("h", "horse");
SortedMap<String, String> submap;
submap = map.subMap("b", "g"); // #1 create a backed collection
System.out.println(map + " " + submap); // #2 show contents
map.put("b", "bat"); // #3 add to original
submap.put("f", "fish"); // #4 add to copy
map.put("r", "raccoon"); // #5 add to original - out of range
// submap.put("p", "pig"); // #6 add to copy - out of range
System.out.println(map + " " + submap); // #7 show final contents
[code=java]

[Mike Simmons]

They're out of range for the submap, not the original map. The submap only has keys between "b" and "g" (inclusive of "b" but not of "g") because that's how the submap was created.

#5 is OK because even though "r" is outside submap's range from "b" to "g", "r" isn't being added to the submap, but to the main map. That's fine, as the main map has no restrictions. The submap just won't ever show the "r" entry, as it's out of the submap's range.

#6 causes an error because "p" is outside the submap's range, and the code is specifically trying to add the "p" into the submap. That's not allowed, so you get an error.

[Udara Amarasinghe]

Hi shuba,

I agree with Mike. It's simple on line 4 you have made submaps range only from 'b' to 'g'(but actually 'f'). So you can only add keys range of 'b' to 'f'. But you have try to add keys like 'r' and 'p' they are not in the key range of submap. That's why you got that IllegalArgumentExceptions.

[shuba gopal]

Hi Mike and Udara, thanks

[Rob Spoor]

Note that this behaviour is documented in the Javadoc page of SortedMap, NavigableMap and TreeMap.