jshell> Long a = 12l; Long b = 12l;
a ==> 12
b ==> 12
jshell> a == b
$3 ==> true
jshell> a = 54321l; b = 54321l;
a ==> 54321
b ==> 54321
jshell> a == b
$6 ==> false
`Long` is a boxed (reference) type, but small numbers are interned so you get the same reference when boxing a primitive value. Larger numbers aren't interned, so you get fresh boxes.
Reference comparison it is with a twist: the jvm caches the most common integers. You'll get the same object from -128 to +127 when implicitly assigning value. This is part of the spec, and can be set to a larger pool with -XX:AutoBoxCacheMax (but cannot be turned off).
If you explicitly ask for a new object (Long a = new Long(123l);) you will get a new object and the comparison will fail as expected.
The moral of the story is to always use .equals().
