Find top 10 students mark using array of object - arrays

Question

I recently had an interview,they asked me a small question
the question is follows
There is list of Students
List<Student> students;
Class Student{
String rollNo;
Map<String, Integer> marks ;
}
Stdunt.marks is actually cobination of subject and mark
Should write an method which should return top 10 students array according to the subject.
List<Student> getTop10(String subjectName){
}

Answer 1

The answer i have given is blelow
private static void PrintTop5(ArrayList<Student> list,String subject){
Collections.sort(list, new Comparator<Student>() {
#Override
public int compare(Student st1, Student st2) {
// TODO Auto-generated method stub
return st2.getSubjectMark(subject) - st1.getSubjectMark(subject);
}
});
ArrayList<Student> studentList = new ArrayList<Student>(list.subList(0,5));
for(Student student : studentList){
System.out.println(student.getRollNum() + " MARK : "+student.getSubjectMark(subject));
}
}
Student class look like below
package com.main;
import java.util.HashMap;
public class Student {
private String rollNo;
private HashMap<String, Integer> marks ;
public Student(){
marks = new HashMap<>();
}
public void setRollNumber(String number){
this.rollNo = number;
}
public void setSubjectAndMark(String subName,int mark){
this.marks.put(subName, mark);
}
public HashMap<String, Integer> getAllMarks(){
return marks;
}
public int getSubjectMark(String subject){
return marks.get(subject);
}
public String getRollNum(){
return rollNo;
}
}

Answer 2

In general your idea is correct, to sort the entire list and take top N students, in fact with java 8 it would look cleaner.
private static void PrintTop5(ArrayList<Student> list,String subject){
list.sort(Comparator
.comparing((Student student) -> student.getSubjectMark(subject))
.reversed());
List<Student> studentList = list.stream().limit(5).collect(Collectors.toList());
for(Student student : studentList){
System.out.println(student.getRollNum() + " MARK : "+student.getSubjectMark(subject));
}
}