maximum Integer value problem with HashMap(String, Integer)?

[paul reberg]

Hi. I have

Map<String, Integer> numbPdfMap=new HashMap<String, Integer>();
Map<String, Integer> numbTxtMap=new HashMap<String, Integer>();		
		
numbPdfMap.put("myKey", 128);
numbTxtMap.put("myKey", 128);    	
    	
if (numbPdfMap.get("myKey") != numbTxtMap.get("myKey"))
	System.out.println("error");		
else
	System.out.println("success");	

I've noticed that if the value for myKey is over 127 (2^7-1), then I get the error message. Otherwise, if it's 127 or less, I'll get the success message. Why does this happen? And, what would you do in situations where the value is more than 128 (2^7)?

Thanks!

[Pat Farrell]

I am surprised that any of your tests get success. You need to use the "equals()" function, not ==

[paul reberg]

ah, brain fart. yeah, you're right. i want to compare the values, not whether they're referring to the same object. however, the part that still confuses me is that they're clearly both different, distinct objects, which SHOULD mean != will always return true. But, if you test out the code, != will return either true or false depending on what you store as the value. Seems pretty odd, right?

[David Newton]

Constant pooling for values < 128.

(Wouter's answer is better-I just hate typing on the iPad :)

[Wouter Oet]

It returns false because you use autoboxing to create your Integer objects.
Autoboxing uses the method Integer.valueOf(int) to create Integer objects.
That method use a cache and because of that, and the fact that Integer object are immutable, you get the same objects. So != returns false.

The range of that cache is -128 to 127 or the value set with java.lang.Integer.IntegerCache.high property with a minimum of 127.

[paul reberg]

ahhh, i c. Ok, thanks alot for the insight!

[Rob Spoor]

paul reberg wrote:ahhh, i c. Ok, thanks alot for the insight!

Sorry to be nitpicking, but it's "I see", not "i c". Please UseRealWords.