Why Integer class caching values in the range -128 to 127?

Question

Regarding my previous Question, Why do == comparisons with Integer.valueOf(String) give different results for 127 and 128? , we know that Integer class

Answer 1

The reason for caching small integers, if that's what you're asking, is that many algorithms use small integers in their calculations, so avoiding the object-creation overhead for these values tends to be worthwhile.

The question then becomes which Integers to cache. Again, speaking in general, the frequency with which constant values are used tends to decrease as the absolute value of the constant increases -- everyone spends a lot of time using the values 1 or 2 or 10, relatively few few use the value 109 very intensively; fewer will have performance depend on how quickly one can obtain an Integer for 722.. Java chose to allocate 256 slots spanning the range of a signed byte value. This decision may have been informed by analyzing programs in existence at the time, but is just as likely to have been a purely arbitrary one. It's a reasonable amount of space to invest, it can be accessed rapidly (mask to find out if the value's in the cache's range, then a quick table lookup to access the cache), and it will definitely cover the most common cases.

In other words, I think the answer to your question is "it isn't as subjective as you thought, but the exact bounds are largely a rule-of-thumb decision ... and experiemental evidence has been that it was good enough."