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Right now I have my array sorting (which is better than getting an error) except it is sorting in the reverse than what I want it to sort in.

   public static void sortDatabase(int numRecords, String[] sDeptArr, 
              int[] iCourseNumArr, int[] iEnrollmentArr)
   {
       System.out.println("\nSort the database. \n");
       String sTemp = null;
       int iTemp = 0;
       int eTemp = 0;
       String a, b = null;
       for(int i=0; i<numRecords; i++)
       {
           int iPosMin = i+1;
           for(int j=iPosMin; j<numRecords; j++)
           {
               a = sDeptArr[i];
               b = sDeptArr[iPosMin];
               if(a.compareTo(b) > 0)
               {
                   sTemp= sDeptArr[j];
                   sDeptArr[j] = sDeptArr[iPosMin];
                   sDeptArr[iPosMin] = sTemp;
                   iTemp = iCourseNumArr[j];
                   iCourseNumArr[j] = iCourseNumArr[iPosMin];
                   iCourseNumArr[iPosMin] = iTemp;
                   eTemp = iEnrollmentArr[j];
                   iEnrollmentArr[j] = iEnrollmentArr[iPosMin];
                   iEnrollmentArr[iPosMin] = eTemp;
               }
               else if(sDeptArr[j].equals(sDeptArr[iPosMin]) && !(iCourseNumArr[j] < iCourseNumArr[iPosMin]))
               {
                   sTemp= sDeptArr[i];
                   sDeptArr[i] = sDeptArr[iPosMin];
                   sDeptArr[iPosMin] = sTemp;
                   iTemp = iCourseNumArr[i];
                   iCourseNumArr[i] = iCourseNumArr[iPosMin];
                   iCourseNumArr[iPosMin] = iTemp;
                   eTemp = iEnrollmentArr[i];
                   iEnrollmentArr[i] = iEnrollmentArr[iPosMin];
                   iEnrollmentArr[iPosMin] = eTemp;
               }
               else continue;
           }

       }
   }

Again, no array lists or array.sorts. I need just to reverse how this is sorting but I have no idea how.

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3 Answers 3

Reset to default
3

just do a.compareTo(b) < 0 instead of the > 0

EDIT: I've figured out the problem. But since this is homework (thanks for being honest), I won't post my solution, but here are a few tips:

  • You are doing selection sort. The algorithm isn't as complicated as you made it. You only have to swap if the two elements you are checking are in the wrong order. I see you have 3 branches there, no need.

  • Take a look at when you are assigning a and b. Through the inner loop, where j is changing, a and b never change, because i and iPosMin stay the same. I hope that helps.

  • It's always good to break your algorithm down to discreet parts that you know works by extracting methods. You repeat the same swap code twice, but with different arguments for indices. Take that out and just make a:

-

// swaps the object at position i with position j in all arrays
private static void swap(String[] sDeptArr, int[] iCourseNumArr, int[] iEnrollmentArr, int i, int j)

Then you'll see you're code get a lot cleaner.

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1 Comment

In that case I can only say that your algorithm isn't sorting at all. If it's sorting properly and always reversed, my solution will work. I've just run your program verbatim and it doesn't sort.
2

First I'd say you need to build a data structure to encapsulate the information in your program. So let's call it Course.

public class Course {
   public String department;
   public Integer courseNumber;
   public Integer enrollment;
}

Why not use the built in sort capabilities of Java?

List<Course> someArray = new ArrayList<Course>();
...
Collections.sort( someArray, new Comparator<Course>() {
    public int compare( Course c1, Course c2 ) {
       int r = c1.compareTo( c2 );
       if( r == 0 ) { /* the strings are the same sort by something else */
          /* using Integer instead of int allows us 
           * to compare the two numbers as objects since Integer implement Comparable
           */
          r = c1.courseNumber.compareTo( c2.courseNumber );
       }
       return r;
    }
});

Hope that gets you an A on your homework. Oh and ditch the static Jr. Maybe one day your prof can go over why statics are poor form.

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4 Comments

NO go away! I don't need that stuff here. I have to do it the way that I am going for, no array lists or stuff. JK but seriously I cant use that.
Well I'll give you a hint. Don't shuffle your array around until you get to the end of the inner loop. So just keep track of the integer that is the smallest according to your comparisons. Then after the inner loop has found the smallest thing in that pass. Swap it with the object at i. This is all much easier if you just use a Course object instead of parallel arrays. You are comparing a and b, but a comes from index i. Then in your shuffling you're using j. Looks wrong.
@Chad But you can still use objects right? You can still sort with your algorithm, but now you don't have three arrays to deal with, only one. Cleans up your code a lot. A lot of times stupid bugs are exposed by just simple refactorings (changes in code that preserve behavior)
@Chad, If you want people to help you with your homework, you need to be a bit more considerate. People are trying to help you for free, to do work you might be expected to do on your own, you shouldn't forget that.
1

Hmm... I wonder what would happen of you altered the line that reads if(a.compareTo(b) > 0)?

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2 Comments

What did you change it to? Are there any other things you could change it to? Do items that are sorted incorrectly give you any hints? Could you change anything else in the code to sort in reverse?
I changed it to < and it sorts differently every time i change it

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