Re: Sorting on Multiple Columns

From: xarax (xarax_at_email.com)
Date: 01/19/05 

Date: Tue, 18 Jan 2005 23:20:50 GMT

"jr" <jrolandumuc@yahoo.com> wrote in message
news:1106088810.003566.6050@z14g2000cwz.googlegroups.com...
> Hi. I'm fairly new to Java and just tried for the first time today to
> sort a data set by multiple columns. I found many solutions for
> sorting on a single column, but none on how to sort on multiple columns
> (none that made sense to my tragically small understanding of Java
> programming, anyway). I think I may have finally found a solution, but
> it may be highly inefficient, full of pitfalls, etc. I'd appreciate
> any advice concerning my simple below, and if this approach is at all
> correct.
>
> The goal of the classes is simply to create a few student objects, and
> then sort them by student id, first name, middle initial, and then last
> name.
>
> Thanks!
>
/snip/

/***************** Sortable Student Class ***************/
import java.util.*;

public class Student
implements Comparable
{
    private static class StudentComparator
    implements Comparator
    {
        public int compare(final Object obj_1, final Object obj_2)
        {
            final Student student_1;
            final Student student_2;

            student_1 = (Student) obj_1;
            student_2 = (Student) obj_2;

            return student_1.compareTo(student_2);
        }
    }

    public static final Comparator STUDENT_COMPARATOR = new StudentComparator();

    /* Instance variables */
    public final int student_id;
    public final String last_name;
    public final String mi;
    public final String first_name;

    /* Object constructor */
    public Student(final int theStudentId, final String theFirstName, final
String theMi, final String theLastName)
    {
        super();

        student_id = theStudentId;
        first_name = theFirstName;
        mi = theMi;
        last_name = theLastName;
    }

    public int compareTo(final Student theStudent)
    {
        final int theId;
        final String theFirstName;
        final String theMi;
        final String theLastName;
        int result;

        theId = theStudent.student_id;
        theFirstName = theStudent.first_name;
        theMi = theStudent.mi;
        theLastName = theStudent.last_name;

        result = (student_id == theStudent_id) ? 0 :
            ((student_id < theStudent_id) ? -1 : 1);
        if(0 == result)
        {
            result = last_name.compareToIgnoreCase(theLastName);
            if(0 == result)
            {
                result = mi.compareToIgnoreCase(theMi);
                if(0 == result)
                {
                    result = first_name.compareToIgnoreCase(theFirstName);
                }
            }
        }
        return result;
    }

    public int compareTo(final Object theObject)
    {
        final Student student;

        student = (Student) theObject;
        return compareTo(student);
    }

}

/**************************************************/

/***************** Caller Program ***************/
import java.util.*;

public class TryStudent
{

    public static void main(String[] args)
    {
        /* Create an array of Student objects */
        Student[] s = new Student[5];

        s[0] = new Student(1,"Joe", "I.","Richards");
        s[1] = new Student(1,"Joe", "I.","Mitchell");
        s[2] = new Student(3,"John","A.","Adams");
        s[3] = new Student(2,"Jake","R.","Scott");
        s[4] = new Student(1,"Jack","B.","Nimble");

        /* Sort array */
        Arrays.sort(s,Student.STUDENT_COMPARATOR);

        /* Print out sorted values */
        for(int i = 0; i < s.length; i++)
        {
            System.out.println(s[i].student_id + " " +
                s[i].first_name + " " +
                s[i].mi + " " +
                s[i].last_name);
        }
    }
}
/*********************************************************/

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