Comparing Alphanumeric Strings From Object Array

Question

Posting a revised question from my original, found at at Sorting Arrays Using Variables Within the Array Basically, I cannot seem to find a method for sorting my array based on the eventCodeString of my Event class. Because the string is alphanumeric (e.g. A123, B321, C222) the conventional Comparator (which I just discovered, thanks to the person in the original post) does not work. The more solutions I come across and try to implement, the more confused I become. Please assist me in understanding the logic of array object comparisons involving strings.

package Chapter9;
import Chapter9.Event;
import javax.swing.JOptionPane;
import java.util.*;
public class EventDemo
{

    public static void main(String[] args)
    {
        callMotto();
                int x, sortMethod;
                Event[] eventStuff = new Event[8];
                for(x = 0; x < 8; ++x)
                {
                    eventStuff[x] = new Event();
                    eventStuff[x].setEventCodeString();
                    eventStuff[x].setGuests();
                    eventStuff[x].setContactNumber();
                    eventStuff[x].setEventStr();
                }
                //Sorting method start
                do
                {
                    String sorting;

                    sorting = JOptionPane.showInputDialog("Please choose sorting method:\n"
                            + "1 to sort by event number\n"
                            + "2 to sort by number of guests\n"
                            + "3 to sort by event type\n"
                            + "Type 99 to exit sorting list");
                    sortMethod = Integer.parseInt(sorting);
                    //Event code sorting start
                    if(sortMethod == 1)
                    {   
                        for(x = 0; x < 8; ++x)
                        {

                        } 
                    }
                    //Event code sorting end
                    if(sortMethod == 2)
                    {
                        for(x = 0; x < 8; ++x)
                        {
                            Arrays.sort(eventStuff, new Comparator<Event>() 
                            {
                                @Override
                                public int compare(Event o1, Event o2) 
                                {
                                    if (o1.getGuests() < o2.getGuests())
                                        return -1;
                                    else if (o1.getGuests() == o2.getGuests())
                                        return 0;
                                    else
                                        return 1;
                                }                                   
                            });
                            eventStuff[x].largeParty();
                        }
                    }
                    //Event type sorting start
                    if(sortMethod == 3)
                    {
                        for(x = 0; x < 8; ++x)
                        {
                            Arrays.sort(eventStuff, new Comparator<Event>() 
                            {
                                @Override
                                public int compare(Event o1, Event o2) 
                                {
                                    if (o1.getEventStr() < o2.getEventStr())
                                        return -1;
                                    else if (o1.getEventStr() == o2.getEventStr())
                                        return 0;
                                    else
                                        return 1;
                                }                                   
                            });
                            eventStuff[x].largeParty();
                        }
                    //Event type sorting end
                //Sorting method end
                    }
                    if(sortMethod == 99)
                        System.exit(0);
                }
                while(sortMethod != 99);
        }   
    public static void callMotto()
    {

        JOptionPane.showMessageDialog(null, "*******************************************************\n"
                        +   "* Carly's Makes The Food That Makes The Party! *\n"
                        +   "*******************************************************");

    }

}

What kind of sort do you want, simple character value sort, or do you want, eg, "X-123" to sort after "X-13"? — Hot Licks
– Hot Licks, Commented Apr 4, 2014 at 22:38
I need the array sorted as follows: assuming the user enters some arbitrary values, say B111, A222, C333, C222, E555, and E111, I would like the output to be A222, B111, C222, C333, E111, E555. — Corey McDonald
– Corey McDonald, Commented Apr 4, 2014 at 22:46
That's just plain alphanumeric sort, what is the difficulty? You just have to understand that only "primitives" can be compared with > < ==, and for objects you need to use an object-specific compare method. String has such a method, named compareTo, or you can use compareToIgnoreCase if you wish. — Hot Licks
– Hot Licks, Commented Apr 4, 2014 at 22:57

Community · Accepted Answer · 2017-05-23 12:20:53Z

2

It's simply because you can't compare Strings using ==, you should use String#equals instead. Same goes for <, <=, !=, > and >=.
You could refer to this other StackOverflow question for explanations.

That is, you have to replace:

Arrays.sort(eventStuff, new Comparator<Event>() {
    @Override
    public int compare(Event o1, Event o2) 
    {
        if (o1.getEventStr() < o2.getEventStr())
            return -1;
        else if (o1.getEventStr() == o2.getEventStr()) // this line
            return 0;
        else
            return 1;
    }                                   
});

by:

Arrays.sort(eventStuff, new Comparator<Event>() {
    @Override
    public int compare(final Event o1, final Event o2) {
        return o1.getEventStr().compareTo(o2.getEventStr));
    }                                   
});

That String#compareTo(String) method comes from the fact that Java Strings implement Comparable<String>, which basically means that they inherently know how to compare themselves.

Since I'm at it, I would suggest you to also change the implementation of that Comparator on guests numbers:

if (o1.getGuests() < o2.getGuests())
    return -1;
else if (o1.getGuests() == o2.getGuests())
    return 0;
else
    return 1;

could become:

return o1.getGuests() - o2.getGuests;

If you think about it, it will indeed:

return a negative value when o1.getGuests() < o2.getGuests()
return 0 when o1.getGuests() == o2.getGuests()
return a positive value when o1.getGuests() > o2.getGuests()

... which is exactly what we need :)

edited May 23, 2017 at 12:20

CommunityBot

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answered Apr 4, 2014 at 22:45

ccjmne

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1 Comment

Corey McDonald Over a year ago

Not only have you answered my question, but you cleaned up my code, as well. Thank you for the assistance, I've been at this for 5 hours.

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