The below code passed the test when run in Java 7 but not in Java 15 environment. Why? I cannot understand the reason? Is this just a bug?

public class Solution { public static void main(String[] args) { Class student = Student.class;

    Method[] methods = student.getDeclaredMethods(); 

    ArrayList<String> methodList = new ArrayList<>();
    for (Method method : methods) {
        methodList.add(method.getName()); 
    }

    Collections.sort(methodList); 
    for (String name : methodList) {
        System.out.println(name); 
    }
}

}