Form biggest number (doubt for java)

i am not able to understand the logic he has used in his code. i refered this code of c++.
can you please help me in this an explain me the approach. basically i havent understood from the sort function, how and why it is used and how it is running.

i can tell you the logic…

Simply sorting doesn’t work. For example, 548 is greater than 60, but in output 60 comes before 548. As a second example, 98 is greater than 9, but 9 comes before 98 in output.

The idea is to use any comparison based sorting algorithm(bubble sort for ex). In the used sorting algorithm, instead of using the default comparison, write a comparison function myCompare() and use it to sort numbers. Given two numbers X and Y, how should myCompare() decide which number to put first – we compare two numbers XY (Y appended at the end of X) and YX (X appended at the end of Y). If XY is larger, then X should come before Y in output, else Y should come before. For example, let X and Y be 542 and 60. To compare X and Y, we compare 54260 and 60542. Since 60542 is greater than 54260, we put Y first.

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