HashMap should be unsorted but still sorts according to key

Question

According to these:

1. http://docs.oracle.com/javase/6/docs/api/java/util/HashMap.html
2. Difference between HashMap, LinkedHashMap and TreeMap
3. jav

Answer 1

Mine is an educated guess, but the reason is likely to be the fact that the default hashCode method uses the memory location. The memory location of small Integers (and your keys are autoboxed into Integer) are most likely fixed: it would be nonesense to have Integer.valueOf(1) return a different memory location on multiple calls. Finally, most likely these fixed memory locations are in the ascending order. This would explain this coincidence, but well, one would need to dig into the implementation of Integer and HashMap to prove this.

Correction: in case of Integer "A hash code value for this object, equal to the primitive int value represented by this Integer object." (JavaDoc). Which, although a different number, confirms the idea.