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This code uses == to compare two integer Integer objects. According to EXP03-J. Do not compare String objects using equality or relational operators, for == to return true for two object references, they must point to the same underlying object. Results of using the == operator in this case will be misleading.
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In this noncompliant code example, it is desired to count the integers of arrays list1 and list2. As class Integer can only cache caches integers from -127 to 128, when an int number value is beyond this range, it is autoboxed into the corresponding wrapper type. The == operator returns false when these distinct wrapper objects are compared. As a result, the output of this example is 0.
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If it were possible to expand the Integer cache inside Integer (cache (for example, caching all the integer values -32K -– 32K, which means that all the int values may in the example would be autoboxed to the same cached Integer object objects), then the results may have differed.
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