Sorting Objects in ArrayList giving unexpected results

Question

Here record is an ArrayList of objects of the type Employee. I am trying to sort the ArrayList based on the employeeName attribute. Unfortunately, it gives unwanted results.

public void sortByName(){       
    for(int i = 0; i < SalesDataManager.N; i++){
        for(int j = i+1; j < SalesDataManager.N; j++){              
            if(record.get(i).getEmployeeName().compareToIgnoreCase(record.get(j).getEmployeeName()) > 0){                           
                Employee etemp = record.get(i);
                record.add(i,record.get(j));
                record.add(j,etemp);                    
            }                       
        }           
    }       
    displayAllRecords();
}

I have gone through other posts in stackoverflow regarding this topic and found out that most of the post suggest this same way.Am I doing something wrong here?

Thanks in advance!

Is modifying the list as iterating through it your intended action? — user2829759
– user2829759, Commented May 14, 2015 at 5:41
It looks like that you want to swap record.get(i) and record.get(j); however, what record.add(position, element) does is inserting the element at the specified position and shifting the original element at that position and any subsequent elements to the right. — Howard Wang
– Howard Wang, Commented May 14, 2015 at 5:47
@HowardWang exactly. You spotted it! I want to swap the two objects and I am getting repeated values. Could you suggest something ? — radiopassive
– radiopassive, Commented May 14, 2015 at 5:50

Mureinik · Accepted Answer · 2015-05-14 05:44:36Z

3

You are iterating the record list and according to some condition determining where to add the current element. However, you aren't emptying the list first, so this approach will inevitably lead to duplications.

Java, luckily, has a built it mechanism for such sorting - you just need to implement a Comparator:

public class EmployeeNameComparator implements Comparator<Emplyoee> {
    @Override
    public int compare (Employee a, Employee b) {
        return a.getEmployeeName().compareToIgnoreCase(b.getEmployeeName());
}

And then just use it:

Collections.sort (record, new EmployeeNameComparator());

If you're using Java 8, you could also use the new cleaner syntax:

Collections.sort
  (record, (a, b) -> a.getEmployeeName().compareToIgnoreCase(b.getEmployeeName());

answered May 14, 2015 at 5:44

Mureinik

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1 Comment

radiopassive Over a year ago

Unfortunately, I cannot use the inbuilt sort method. It's an assignment and I have to do it the classic way! There are duplicates as you have mentioned, which probably is due to the add(index, object) method of ArrayList. I want to swap the position of objects.

radiopassive · Accepted Answer · 2015-05-14 06:10:36Z

@Howard Wang and Mureinik, you guys were right. The add(index,object) method added the object to the index and was right-shifting the already existing object, instead of replacing it, which was what I was intending to achieve. So, adding record.remove(i+1); and record.remove(j+1); to the code did the trick!

public void sortBySales()
{



    for(int i = 0; i < SalesDataManager.N; i++)
    {
        for(int j = i+1; j < SalesDataManager.N; j++)
        {

            if(record.get(i).getEmployeeSales() > record.get(j).getEmployeeSales())
            {


                Employee etemp = record.get(i);
                record.add(i,record.get(j));
                record.remove(i+1);
                record.add(j,etemp);
                record.remove(j+1);

            }   

        }

    }




}

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