Sorting objects using Collections.sort(). Getting an error

Question

I'm trying to sort a list of objects in java using Collections.sort(). But I keep getting this error: type parameter is not within its bound". Does anyone know how I can remedy this problem?

My code

   public List<String> fetchNumbersForLeastContacted()
   {


    List<String> phonenumberList = getUniquePhonenumbers();
    List<TopTen> SortList = new ArrayList<TopTen>();


    Date now = new Date();
    Long milliSeconds = now.getTime();

    //Find phone numbers for least contacted
    for (String phonenumber : phonenumberList)
    {



       int outgoingSMS = fetchSMSLogsForPersonToDate(phonenumber, milliSeconds).getOutgoing();
       int outgoingCall = fetchCallLogsForPersonToDate(phonenumber, milliSeconds).getOutgoing();

       //Calculating the total communication for each phone number
       int totalCommunication = outgoingCall + outgoingSMS;

       android.util.Log.i("Datamodel", Integer.toString(totalCommunication));

       SortList.add(new TopTen(phonenumber, totalCommunication, 0));

    }

    //This is where I get the error
   Collections.sort(SortList);

The TopTen.class

public class TopTen {

private String phonenumber;
private int outgoing;
private int incoming;


public TopTen (String phonenumber, int outgoing, int incoming)
{
    this.phonenumber = phonenumber;
    this.incoming = incoming;
    this.outgoing = outgoing;


}

public String getPhonenumber() {
    return phonenumber;
}

public void setPhonenumber(String phonenumber) {
    this.phonenumber = phonenumber;
}

public int getOutgoing() {
    return outgoing;
}

public void setOutgoing(int outgoing) {
    this.outgoing = outgoing;
}

public int getIncoming() {
    return incoming;
}

public void setIncoming(int incoming) {
    this.incoming = incoming;
}}

Vikram · Accepted Answer · 2013-09-28 07:06:42Z

public static void sort (List<T> list)

This method can only be used if T inplements the Comparable interface. What implements Comparable means is that there exists a criteria by which two objects of type T can be compared and ordered. In your case, T is TopTen, which does not implement Comparable.

What you need to do:

public class TopTen  implements Comparator<TopTen> {

    ....
    ....

    @Override
    public int compareTo(TopTen other) {

        if (this == other) return EQUAL;

        return this.getPhonenumber().compareToIgnoreCase(other.getPhonenumber());

    }

This will compare two TopTen objects based on the phonenumber field. If you want the objects to be ordered based on another criteria, use that to return either -1 (before), 0 (equal) or 1 (after).

For example, to base the sorting on incoming, use the following:

@Override
public int compareTo(TopTen other) {

    final int BEFORE = -1;
    final int EQUAL = 0;
    final int AFTER = 1;

    if (this == other) return 0;

    if (this.getIncoming() > other.getIncoming()) {
        return AFTER;
    } else if (this.getIncoming() < other.getIncoming()) {
        return BEFORE;
    } else {
        return EQUAL;
    }

}

This would get you TopTen objects ordered by ascending incoming field values.

upog · Accepted Answer · 2013-09-28 06:00:02Z

0

try implementing Comparable interface in TopTen class and override compareTo method to specify your sorting logic

@Override
public int compareTo(TopTen o) {
    // TODO Auto-generated method stub
    return 0;
}

(or)

Collections.sort(SortList, new Comparator<TopTen>(){
            public int compare(TopTen t1, TopTen t2) {
                return t1.phonenumber.compareTo(t2.phonenumber);
            }
        });

edited Sep 28, 2013 at 6:00

answered Sep 28, 2013 at 5:53

upog

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