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    new Integer(10) == new Integer(10) // true

Before value classes this would always be false. The only time comparing Integer objects with == could be true is if Integer object was create by going through Integer.valueOf (or obviously if they were the same object reference.) By default the cached values where -127 to 127, but that is tuneable at runtime.

https://github.com/openjdk/jdk/blob/jdk-27%2B27/src/java.bas...

by tsimionescu6 hours ago|

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It could also be true if the instances were created through auto-boxing (e.g. arrayList.add(10); arrayList.add(10); arrayList.get(0) == array List.get(1) //would return true, but false if you used 1000 instead of 10).

by papercrane5 hours ago|

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Yes, because auto-boxing is just compiling to Integer.getValue under the hood, the bytecode for Integer.getValue(1) and ((Integer) 1) is the same. They'll both compile to something like:

   iconst_1
   invokestatic java/lang/Integer.valueOf:(I)Ljava/lang/Integer

by tsimionescu5 hours ago|

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Sure, I was just talking about Java syntax, not the bytecode internals.

by jmyeet4 hours ago|

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So you've made my point in showing how complex this is because you're incorrect [1][2]:

> By default, Java maintains a cache of Integer objects for values between -128 and +127.

[1]: https://stackoverflow.com/questions/3130311/weird-integer-bo...

[2]: https://dev.to/marzuk16/understanding-integer-caching-in-jav...

by xxs4 hours ago|

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it's easier to remember that it originated from the Byte range, where all bytes could be kept in. Character didn't have negative values so it did [0-128) instead. Long and Short are the same as Byte.

Years before the autoboxing/Integer.valueOf() caching stuff (and before generics), (I) used to have IntegerProvider that did similar stuff to higher ranges. Personally, I have considered autoboxing on integers net-negative for Java