My program works fine, but i'm not sure why it works that way.

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So this is probably common in programming world, you write a program, it works but you don't really know how it works :D I need an explanation to one particular part of the program. Why does comparison

list.get(i).equals(list.get(i+1))

return true for integers higher then 127 if values are the same but

list.get(i) == list.get(i+1)

returns false? After all we are comparing integers, not objects so "==" operator should be fine there. "==" operator works as intended for numbers lower then 127. What does the 127 number do, does it magically turn integer simple type into complex type? I don't get it, please explain.

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Robert

Poziom 8 , Warsaw, Poland

25 października 2020, 20:19

Maybe this help You understand: Integer.ValueOf() method creates the java.lang.Integer object by passing the specified ‘int‘ value. Actually, it doesn’t create the new objects for all the values you pass. This method is implemented such that the frequently used values are cached. I.e. internally it maintains an array of Integer objects where Integer objects for frequently requested values are created and stored at the time of VM initialization itself. By default, these values will be from -128 to 127. So, for any number you pass between -128 and 127 (inclusive), it doesn’t create the new Integer object. Instead it returns already cached object from the array. If you pass the number beyond this range, then only it creates a new Integer object. Below is the source code of Integer.valueOf() method.

AnnemiekFF

Poziom 41 , Breda, Netherlands

27 maja 2020, 14:15

127 is the max that fits in a byte.