Sorting and secondary sorting in java using Coamparable interface

Question

I have class called Order where I have getter and setter methods for OrderID and produstID field.

1) I want to get sort orderID in asending order and corresponding productID in desending order. So I used Comparable interface and compareTo methods to do that.I'm able to sort orderID but corresponding productID's are not sorted in descending order(secondary sorting).

Please let me know how can i do that.

Code i have used :

   @Override
public int compareTo(Order ord)
{
    double orderId1 = ((Order) ord).getOrderId();
    return (int) (this.orderId - orderId1);
    //return orderId.equals(ord.orderId);
}

2) I wanted to search based on orderID and want to get corresponding productid's.

Here I'm using hard coded data.

My data lokks like this:

Order data:

orderID  productID
1001        22
1003        33
1001         33

Desired output for soring is :

 orderID  productID
1001        33
1001        22
1003        33

Show the code where you use the comparator to sort the collection. — Upio
– Upio, Commented Apr 10, 2015 at 6:22

Jens · Accepted Answer · 2015-04-10 06:51:38Z

3

I think this should work:

public int compareTo(Order ord)
{
    if (this.orderId == ord.getOrderId()){
       return (int) (ord.getProductId() - this.productId);
    }
    return  this.orderId - ord.getOrderId();
}

if have to compare the productId only if the is orderId equals.

edited Apr 10, 2015 at 6:51

answered Apr 10, 2015 at 6:23

Jens

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Comments

maba · Accepted Answer · 2015-04-10 06:43:36Z

1

Best way is to use built-in functions for comparing.

@Override
public int compareTo(Order o) {
    int d = Double.compare(this.getOrderId(), o.getOrderId());
    if (d == 0) {
        d = Double.compare(o.getProductId(), this.getProductId());
    }
    return d;
}

But I don't really think that your orderId and productId should be of double type. Better have them as int. If you change to int then still use the built-in comparators, just change to Integer.compare(x,y).

answered Apr 10, 2015 at 6:43

maba

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7 Comments

shree11 Over a year ago

Hey thank you so much. Sorting and secondary sorting is working fine. But how can i search based on orderId and get corresponding productID. Here if i create method called SearchByOrderid(), then when i pass orderid as 1001, then i should get all the prodid's attached to that. How can i do this.

maba Over a year ago

@shree11 That depends on what kind of collection you are using. Can you update your question with that information?

shree11 Over a year ago

Here i'm using List<Order> OrderList= new ArrayList<Order>();. Here have created method called SearchByOrderID(Order id); So whenever i pass the OrderID, i should get all the productID's attached to it.

maba Over a year ago

@shree11 I think you'll need to use a TreeMap instead and then you can use TreeMap#subMap to get a partial view of the TreeMap with all the objects you are interrested in.

shree11 Over a year ago

Can i do like this : public Order1 SearchByOrderID(int o) { //logic for search } and main method call SerachByOrderID. But i do not know how to do it

|

Mateusz Sroka · Accepted Answer · 2015-04-10 06:41:43Z

0

You could try this:

@Override
public int compareTo( Order ord )
{
    if( this.orderId != ord.getOrderId() )
    {
        return Double.compare( this.orderId, ord.getOrderId() );
    }
    return Double.compare( ord.getProductId(), this.productId );
}

answered Apr 10, 2015 at 6:41

Mateusz Sroka

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Comments

Giovanni · Accepted Answer · 2015-04-10 06:48:29Z

Here is a sample with your data that orders the items

package test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class TestOrder {

    public static void main(String[] args) {
        List<OrderProduct> myList=new ArrayList<>();
        myList.add(new OrderProduct(22, 1001));
        myList.add(new OrderProduct(33, 1003));
        myList.add(new OrderProduct(33, 1001));
        Collections.sort(myList);
        for (OrderProduct op : myList) {
            System.out.println(op.getOrderId() + " " + op.productId);
        }

    }

    private static class OrderProduct implements Comparable<OrderProduct>{
        private int productId;
        private int orderId;

        public OrderProduct(int productId, int orderId) {
            super();
            this.productId = productId;
            this.orderId = orderId;
        }


        public int getProductId() {
            return productId;
        }
        public int getOrderId() {
            return orderId;
        }


        @Override
        public int compareTo(OrderProduct o) {
            if (o==null) {
                return 1;
            }
            if (orderId==o.orderId) {
                return o.productId-productId;
            }
            return orderId-o.orderId;
        }
    }

}

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