👀 Views: 45 💬 Answers: 1 📅 Created: 2025-06-13

sorting merge-sort comparator Java

I'm upgrading from an older version and I'm deploying to production and I recently switched to I'm following best practices but I'm currently implementing a merge sort algorithm in Java, and I've introduced a custom comparator to sort objects of a class `Employee` based on their salary... However, I'm encountering unexpected behavior where the sorted output does not seem to reflect the proper order according to the comparator. Here’s the relevant code snippet: ```java import java.util.Comparator; class Employee { String name; int salary; Employee(String name, int salary) { this.name = name; this.salary = salary; } } public class MergeSort { public static void mergeSort(Employee[] employees, Comparator<Employee> comparator) { if (employees.length < 2) return; int mid = employees.length / 2; Employee[] left = new Employee[mid]; Employee[] right = new Employee[employees.length - mid]; System.arraycopy(employees, 0, left, 0, mid); System.arraycopy(employees, mid, right, 0, employees.length - mid); mergeSort(left, comparator); mergeSort(right, comparator); merge(employees, left, right, comparator); } private static void merge(Employee[] employees, Employee[] left, Employee[] right, Comparator<Employee> comparator) { int i = 0, j = 0, k = 0; while (i < left.length && j < right.length) { if (comparator.compare(left[i], right[j]) <= 0) { employees[k++] = left[i++]; } else { employees[k++] = right[j++]; } } while (i < left.length) { employees[k++] = left[i++]; } while (j < right.length) { employees[k++] = right[j++]; } } } ``` I'm using the following comparator: ```java Comparator<Employee> salaryComparator = (e1, e2) -> Integer.compare(e1.salary, e2.salary); ``` When I run my merge sort on an array of `Employee` objects like this: ```java Employee[] employees = { new Employee("Alice", 30000), new Employee("Bob", 50000), new Employee("Charlie", 40000) }; MergeSort.mergeSort(employees, salaryComparator); ``` The expected output should sort the employees by salary in ascending order, but instead, I see the following order: Alice, Charlie, Bob, which seems incorrect. I’ve double-checked the comparator and it appears to be functioning correctly. I've tried adding print statements within the merge function to trace the values being assigned to the `employees` array, but everything seems to be flowing as expected. I'm using Java 17. Is there something I'm missing in the merge logic that could lead to this unexpected ordering? Any help would be greatly appreciated! I've been using Java for about a year now. Any feedback is welcome! I'm using Java LTS in this project. What am I doing wrong? Any ideas what could be causing this?