Ascending and Desending order in same program using java

Question

I want to sort the data according to id and marks pair. ID should be in ascending order and marks should be in descending order, here is my code:

ArrayList<Student> al=new ArrayList<Student>();
    al.add(new Student(1,"dg",58));
    al.add(new Student(2,"dg",48));
    al.add(new Student(1,"dg",98));
    al.add(new Student(2,"dg",68));
    al.add(new Student(1,"dg",38));
    al.add(new Student(2,"dg",28));
    al.add(new Student(2,"dg",90));    

output like:

1 dg 98  
1 dg 58  
1 dg 38  
2 dg 90  
2 dg 68  
2 dg 48  
2 dg 28  

Answer 1

You have to implement Comparable for the Student class or sort it directly using a custom Comparator:

Comparator<Student> comparator = Comparator
    .comparing(Student::getId)                            // First ID in ascending order
    .thenComparing(Comparator.comparing(Student::getMark) // Then mark 
                             .reversed());                // ... but in descending order

al.sort(comparator);                                      // Here is the sort performed