Java interview: for loop, object/class reference and bound limit [duplicate]

Question

This question came up in one of my interview questions for an internship position written in Java. Notice that the boolean function isSame actually declares 2 parameters as Integer class - not int, so I thought a and b are objects, correct?

public class ForLoop{ public static boolean isSame(Integer a, Integer b) { return a == b; } public static void main(String []args){ int i = 0; for (int j=0; j<500; ++j) { if (isSame(i,j)) { System.out.println("Same i = "+i); System.out.println("Same j = "+j); ++i; continue; } else { System.out.println("Different i = "+i); System.out.println("Different j = "+j); ++i; break; } } System.out.println("Final i = " + i); } }

My first thought is that the for loop would terminate in the 1st run with the result Final i = 1, but to my surprise the final output is i = 129. The loop terminated when both i & j = 128.

 Same i = 126 Same j = 126 Same i = 127 Same j = 127 Different i = 128 Different j = 128 Final i = 129

Can someone please explain?

The answer here will answer your question

Baby
– Baby

2014-10-24 02:23:57 +00:00
Commented Oct 24, 2014 at 2:23 — Baby
– Baby, Commented Oct 24, 2014 at 2:23

Elliott Frisch · Accepted Answer · 2014-10-24 02:16:18Z

When testing Object types for equality use .equals(), as you have found -128 to 127 (inclusive) are pooled. The JLS-5.1.7 says in part,

If the value p being boxed is true, false, a byte, or a char in the range \u0000 to \u007f, or an int or short number between -128 and 127 (inclusive), then let r1 and r2 be the results of any two boxing conversions of p. It is always the case that r1 == r2.

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