Question

Sorting custom Bid type

Asked by: Jazzle

Hi Experts,
 I have created a simple new type:

public class Bid {
    int bidder;
    double price;
    int quantity;

    public Bid(int bidder, double price, int quantity) throws IllegalArgumentException {
        if (price <= 0) throw new IllegalArgumentException("Negative/Zero Price bid/ask");
        if (quantity == 0) throw new IllegalArgumentException("Zero Quantity bid/ask");
        this.bidder = bidder;
        this.price = price;
        this.quantity = quantity;
    }
}

and I wish to collect a number (perhaps up to 1000) of these, and then sort them according to their price and by quantity (separately).
Naturally, I want to keep processing speed high.

How can I best store them (i.e. in an Array?), and then how can I sort them?

MTIA for all suggestions,
 J

(As ever, I will increase the points if this question turns out to be more difficult than expected)

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Asked On
2005-09-06 at 04:37:43ID21551821
Tags

custom

,

sort

Topic

Java Programming Language

Participating Experts
1
Points
175
Comments
10

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Answers

 

by: zzynxPosted on 2005-09-06 at 04:50:15ID: 14828302

>> How can I best store them (i.e. in an Array?),
Put them in an array or an (Array)List

>> and then how can I sort them?
By this:

java.util.Collections.sort(yourList, new java.util.Comparator() {
    public int compare(Object o1, Object o2) {
        Bid b1 = (Bid)o1;
        Bid b2 = (Bid)o2;
        return new Double(b1.getPrice()).compareTo(new Double(b2.getPrice()));
    }
}) ;

or by quantity:

java.util.Collections.sort(yourList, new java.util.Comparator() {
    public int compare(Object o1, Object o2) {
        Bid b1 = (Bid)o1;
        Bid b2 = (Bid)o2;
        return b1.getQuantity()-b2.getQuantity();
    }
}) ;


Of course I assume your Bid class has the getPrice() and getAQuatity() methods

 

by: zzynxPosted on 2005-09-06 at 04:52:50ID: 14828320

So I chose for a List.


List myList = new ArrayList();
myList.add( new Bid(1, 10.0, 5) );
myList.add( new Bid(2, 100.0, 51) );
myList.add( new Bid(3, 1.0, 10) );

Now you have an unsorted list.
To sort by price:

java.util.Collections.sort(myList, new java.util.Comparator() {
    public int compare(Object o1, Object o2) {
        Bid b1 = (Bid)o1;
        Bid b2 = (Bid)o2;
        return new Double(b1.getPrice()).compareTo(new Double(b2.getPrice()));
    }
}) ;

To sort by quantity:

java.util.Collections.sort(myList, new java.util.Comparator() {
    public int compare(Object o1, Object o2) {
        Bid b1 = (Bid)o1;
        Bid b2 = (Bid)o2;
        return b1.getQuantity()-b2.getQuantity();
    }
}) ;

 

by: JazzlePosted on 2005-09-06 at 04:54:55ID: 14828328

I thought it would involve Comparators, but I didn't want to lead it one way.

Can you re-write that so the Comparators are defined elsewhere?

>>Of course I assume your Bid class has the getPrice() and getAQuatity() methods
Actually, those properties are simply public ATM, but I probably ought to change that!

 

by: JazzlePosted on 2005-09-06 at 04:57:51ID: 14828342

[Your second post appeared]
Can you say why you chose a List?
 Is there any significant gain (execution time / coding capabilities) in doing so?

 

by: zzynxPosted on 2005-09-06 at 04:59:02ID: 14828349

>> Can you re-write that so the Comparators are defined elsewhere?
Sure:

public class PriceComparator implements Comparator {
    public int compare(Object o1, Object o2) {
        Bid b1 = (Bid)o1;
        Bid b2 = (Bid)o2;
        return new Double(b1.getPrice()).compareTo(new Double(b2.getPrice()));
    }

    public boolean equals(Object obj) {
        return false;
    }
}

Then to sort:

java.util.Collections.sort(myList, new PriceComparator() );

 

by: zzynxPosted on 2005-09-06 at 05:01:37ID: 14828361

>> Can you say why you chose a List?
Because that Collections.sort() method takes a list (But a sort on arrays also exists afaik)

>> Is there any significant gain (execution time / coding capabilities) in doing so?
Don't know, but don't think so.

>> Actually, those properties are simply public ATM, but I probably ought to change that!
That's good practice, yes

 

by: zzynxPosted on 2005-09-06 at 05:03:11ID: 14828367

Same for QuantityComparator:

public class QuantityComparator implements Comparator {
    public int compare(Object o1, Object o2) {
        Bid b1 = (Bid)o1;
        Bid b2 = (Bid)o2;
        return b1.getQuantity()-b2.getQuantity();
    }

    public boolean equals(Object obj) {
        return false;
    }
}

and

java.util.Collections.sort(myList, new QuantityComparator() );

 

by: JazzlePosted on 2005-09-06 at 05:03:12ID: 14828368

Fantastic, thanks for the speedy replies. :D

 

by: zzynxPosted on 2005-09-06 at 05:03:28ID: 14828370

Thanks

 

by: zzynxPosted on 2005-09-06 at 05:04:15ID: 14828374

...for accepting.
>> Fantastic, thanks for the speedy replies. :D
My pleasure

20120131-EE-VQP-002

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