Strange behaviour: Java Comparator randomizes list entries.

Answer 1

your toString method probably isn't overridden for your objects representing the contacts. It will return a hash string for those objects, which varies every time your app is run.

You can fix this either of two ways:

• Override the toString() method in your Contact object to return the contact's name (1), or
• Change the Comparator to Comparator<Contact> so it gets Contact objects as parameters (2)

for (1), add this to your Contact class:

@Override public String toString() {
    return get_contactFirstName();
}

for (2) you would end up with this Comparator implementation:

final static class ContactsListComparator implements Comparator<Contact> {                           
    public int compare(Contact o1, Contact o2) {
        return contact1.get_contactFirstName().compareTo(contact2.get_contactFirstName());
    }
}

you don't even need to check for the <0 or >0, but you can just return whatever the String comparison gives.

Answer 2

I would use:

final static class ContactsListComparator implements Comparator<Contact>
{
public int compare(Contact c1,Contact c2)
 {
 int i=c1.get_contactLastName().compareTo(c2.get_contactLastName());
 if(i!=0) return i;
 return c1.get_contactFirstName().compareTo(c2.get_contactFirstName());;
 }

}

Answer 3

Your first example is basically the same as

final static class ContactsListComparator implements Comparator {                           
    public int compare(Object o1, Object o2) {
        return o1.toString().compareTo(o2.toString());
    }    
}

This would work if you override toString() like

public String toString() {
     return _contactFirstName + ' ' + _contactLastName;
}

However, a comparator which compares the intended fields is better as has been suggested.