java - Binary optimization search -

i'm trying write function optimize function using binary subdivision. idea can pass lower , upper bounds test , return lowest value of n returns 'true' function.

public interface binarytest {     boolean test(int n); }  /**  * returns smallest int in set lower <= n <= upper returns true  * {@link binarytest#test(int)}. if value 'n' returns true, value  * > 'n' return true.  *  * if none of values return true, return -1.  */ int optimizesmallest(int lower, int upper, binarytest testfunction) {     // ??? } 

while examples of binary search common, more difficult find patterns , feel it's easy end off-by-one error.

what optimizesmallest function like?

simple testcase:

    (int = 0; < 10; i++) {         int j = i;         int r = binarysearch.optimizesmallest(0, 10, (n) -> {             return n > j;         });          assertequals(i + 1, r);     } 

int optimizesmallest(int lower, int upper, binarytest testfunction) {     if (lower > upper || !testfunction.test(upper)) {         return -1;     }     while (lower != upper) {         int middle = (lower + upper) / 2;         if (testfunction.test(middle)) {             upper = middle;         } else {             lower = middle + 1;         }     }     return lower; }