how to sort a list with different attributes in java

Question

I want sort a list of student object containing attributes name and course such that the sorting is done based on name and if two names are same then it should consider course for sorting... I can do it separately but want a single list... PLz help...

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package studentlist;

import java.util.*;

/**
 *
 * @author Administrator
 */
public class StudentList {

    /**
     * @param args the command line arguments
     */
    String name, course;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getCourse() {
        return course;
    }

    public void setCourse(String course) {
        this.course = course;
    }

    public StudentList(String name, String course) {
        this.name = name;
        this.course = course;
    }

    public static void main(String[] args) {
        // TODO code application logic here
        List<StudentList> list = new ArrayList<StudentList>();

        list.add(new StudentList("Shaggy", "mca"));
        list.add(new StudentList("Roger", "mba"));
        list.add(new StudentList("Roger", "bba"));
        list.add(new StudentList("Tommy", "ca"));
        list.add(new StudentList("Tammy", "bca"));

        Collections.sort(list, new NameComparator());
        Iterator ir = list.iterator();

        while (ir.hasNext()) {
            StudentList s = (StudentList) ir.next();
            System.out.println(s.name + " " + s.course);
        }

        System.out.println("\n\n\n ");
        Collections.sort(list, new CourseComparator());
        Iterator ir1 = list.iterator();

        while (ir1.hasNext()) {
            StudentList s = (StudentList) ir1.next();
            System.out.println(s.name + " " + s.course);
        }

    }

}

class NameComparator implements Comparator<StudentList> {

    public int compare(StudentList s1, StudentList s2) {

        return s1.name.compareTo(s2.name);

    }

}

class CourseComparator implements Comparator<StudentList> {

    public int compare(StudentList s1, StudentList s2) {
        return s1.course.compareTo(s2.course);
    }
}

you already know the condition , now apply this in your comparator class — Hussain Akhtar Wahid 'Ghouri'
– Hussain Akhtar Wahid 'Ghouri', Commented Oct 14, 2013 at 7:55

Rohit Jain · Accepted Answer · 2013-10-14 06:27:51Z

6

You just have to put both the comparison in a single Comparator.

First test the name are equal or not:
- If they are not equal, then return the result of comparison of name.
- If they are equal, move to compare the courses:

Following comparator would work:

class NameCourseComparator implements Comparator<StudentList> {

    public int compare(StudentList s1, StudentList s2) {
        if (s1.name.equals(s2.name)) {
            return s1.course.compareTo(s2.course);
        }
        return s1.name.compareTo(s2.name);
    }
}

answered Oct 14, 2013 at 6:27

Rohit Jain

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2 Comments

Tanuj Jeena Over a year ago

its giving the output as: Roger bba Tommy bca Tommy ca Roger mba Shaggy mca i want it as : Roger bba Roger mba Tommy bca Tommy ca Shaggy mca

Rohit Jain Over a year ago

@TanujJeena How are you using it? It's working fine in my case. Are you still sorting it twice? You just need one sort now, with new NameCourseComparator().

CodingBird · Accepted Answer · 2013-10-14 06:27:47Z

3

One simple way:

Sort the list according to the name first. After that loop through the list again. If you find any same name in order, then compare the course and update the list accordingly.

answered Oct 14, 2013 at 6:27

CodingBird

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2 Comments

Mateusz Dymczyk Over a year ago

this is basically doing a sort twice, which isn't necessary

CodingBird Over a year ago

@Mateusz yes it is. I just suggesting a simple way which I thought of when I answered the question. Though it is inefficient, but still it answer the question correctly :)

VikramV · Accepted Answer · 2013-10-14 06:35:20Z

0

You could just tweak the NameComparator a bit

class NameComparator implements Comparator<StudentList> {
      public int compare(StudentList s1, StudentList s2) {
        if(s1.getName().equals(s2.getName()) {
           return s1.getCourse().compareToIgnoreCase(s2.getCourse());
        }else {
           return s1.getName().compareToIgnoreCase(s2.getName());   
      }
}

answered Oct 14, 2013 at 6:35

VikramV

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2 Comments

upog Over a year ago

you should use equals to compare string

VikramV Over a year ago

@upog: Thanks for the correction. I've updated my answer accordingly.

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