How to Sort an Array Object by its attribute

[Volkof]

Hi all,

Lets say I have these classes:
======================================================

public class PlaneSeat {
    //Attributes
    private int seatId;
    private int customerId;
    private boolean assigned;
}

Every Plane Seat has a seatId, and only 1 customer can be assigned to it.

Assigning Seat ..
Please enter SeatID: 10
Please enter Customer ID: 10001
Seat Assigned!
======================================================

Now I have a Plane:

public class Plane {
    //Attributes
    private int totalSeats = 12;
    private PlaneSeat PlaneSeat[];
    private int numEmptySeat = totalSeats;
}

Every Plane can have up to 12 seats
======================================================

Now lets say

SeatID 1 assigned to CustomerID 1009
SeatID 2 assigned to CustomerID 1004
SeatID 3 assigned to CustomerID 1005

However I need to print out in sorted order of CustomerID, so it should become like this:

SeatID 2 assigned to CustomerID 1004
SeatID 3 assigned to CustomerID 1005
SeatID 1 assigned to CustomerID 1009

How do I sort the PlaneSeat objects in ascending order of their CustomerID?
To my knowledge, I should use:

import java.util.Arrays;
 
Arrays.sort()

Something like
Arrays.sort(PlaneSeats, Sort by CustomerID)?


Thanks in advance

 

[Accname]

You should read the JDoc for Comparators:
http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Comparator.html
Then you should be able to write your own comparator, a subclass of the java comparator, which will work with PlaneSeats and sort them.
Then you can call
java.util.Collections.sort(List, Comparator)
java.util.Arrays.sort(Object[], Comparator)
to sort your list or array.

Basically all you need to implement is
compare(Object o1, Object o2)
Which returns an int which is
positive if o1 > o2,
zero if 01 == o2,
and negative if o1 < o2

furthermore sgn(compare(o1, o2) == -sgn(compare(o2, o1)) should be true.

 

[DrEvil]

Just curious, but do you really need the 'private boolean assigned;'
If no customer is assigned to a PlaneSeat the customerID should be some sort of default value (0).
Meaning you could just check whether customerID!=0 (means its assigned...)

 

[Volkof]

@Accname

Yes I did come across Comparator, I know I need it, but dont understand how to use it.

So I'm suppose to create a separate Comparator Class, and define the Sort Algorithm there? But that is the confusing part. How do I even code the Comparator Class?

@DrEvil
I cant use CustomerID. What if it is also set as 0?

 

[s3rius]

Yes, the comparator is a seperate class whose only purpose is to compare two objects of a certain kind.

Here's an example for the comparator class:

public class SortByEmptySeats implements Comparator{
 
    public int compare(Object o1, Object o2) {
        Plane p1 = (Plane ) o1;
        Plane p2 = (Plane ) o2;
        return p1.getEmptySeats() - p2.getEmptySeats();
    }
}

Then you can use the sort() method to sort your container according to your custom comparator.

Collections.sort(  yourListOfPlanes, new SortByEmptySeats()  );