Sort Object by two attributes

Question

Let's say I have a List with Students: ArrayList<Student> student = new ArrayList<>();. The Student-class looks like this:

public class Student {
    String name;
    int age;
    String hobby;

    //getter and Setter methods below
}

I want to sort that list by name, but if the names are equal, I want to sort it after the age. How can I do this in Java.

With this I can already sort it by name:

public class MyComparator implements Comparator<Student>{

    @Override
    public int compare(Student o1, Student o2) {
        if(o1.getName() > o2.getName()){
            return 1;
        }
        else if(o1.getName() < o2.getName())
        {
            return -1;
        }
        else{
            return 0;
        }
    }
}

So if they have the same name, how can I sort it after the age? In the end I want to do Collections.sort(student, MyComparator comp) to sort the list.

Possible duplicate of [Sort ArrayList of custom Objects by property](http://stackoverflow.com/questions/2784514/sort-arraylist-of-custom-objects-by-property) — Han Arantes, Mar 16 '16 at 11:27
My problem is almost the same as the article that you mentoined, but i needed it for two attributes. — member2, Mar 16 '16 at 12:56

score 3 · Accepted Answer · answered Mar 16 '16 at 11:44

This should work:

public class StudentsComparator implements Comparator<Student> {

    @Override
    public int compare(Student s1, Student s2) {
        final int nameComparison = s1.getName().compareToIgnoreCase(s2.getName());
        if (nameComparison != 0) {
            return nameComparison;
        }
        return Integer.compare(s1.getAge(), s2.getAge());
    }

}

You can also make Student comparable:

public class Student implements Comparable<Student> {

    String name;
    int age;
    String hobby;

    @Override
    public int compareTo(Student other) {
        final int nameComparison = name.compareToIgnoreCase(other.name);
        if (nameComparison != 0) {
            return nameComparison;
        }
        return Integer.compare(age, other.age);
    }

}

Thanks thats what i wanted :) – member2 Mar 16 '16 at 12:56 — member2, Mar 16 '16 at 12:56

Sort Object by two attributes

1 Answers1