Maximum value in array containing Objects Java

Question

I have an array named trick of type Card which stores the Suit and the Rank. Is there a way to use Collections.max to find the highest ranked card? I have used ordinals in other aspects of my code but cant seem to get it to work now.

I have tried this, (t is the parameter passed into the method. trick is the array containing the Cards)

Collections.max(t.trick.rank.ordinal());

Its part of an else if statement which then goes onto another so I don't think I can start it with a for loop and as its part of a inherited class I cant do the for loop else where as it throws errors due to it not being inherited from the other class. Is there a simple way of finding my highest ranked card?

Can you add a code sample that illustrates your data structure? Trying to infer that from your prose isn't exactly my favourite activity... — morido, Jan 18 '16 at 20:27
https://docs.oracle.com/javase/7/docs/api/java/util/Collections.html#max%28java.util.Collection,%20java.util.Comparator%29 — user3707125, Jan 18 '16 at 20:30
I think you should post your code if you really need any help — Pritam Banerjee, Jan 18 '16 at 20:31
does your array have a rank as well? why are you doing `t.trick.rank`? `trick` is your array correct? So shouldn't it be something like `t.trick[index].rank`? — gonzo, Jan 18 '16 at 20:36
Do you have to use Collections.max? Stream.max is probably going to be easier. — VGR, Jan 18 '16 at 21:21

ForeverStudent · Answer 1 · 2016-01-18T20:52:41.067

I would recommend you have your Card class implement the Comparable interface. This requires you to define a comparison function between Card instances.

Then all you will need to do to get the "biggest" card is call Collections.max on it.

a complete but minimalistic solution would look like this:

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

public class TestingClass 
{

public static void main(String[] args) throws Exception 
{
    List <Card> a = new ArrayList<Card>();
    a.add(new Card(1));
    a.add(new Card(5));
    a.add(new Card(2));
    a.add(new Card(3));

    Card x= Collections.max(a);
    System.out.println(x.rank); //this will print 5
}

}

class Card implements Comparable<Card>
{
    public int rank;
    public Card(int rank)
    {
        this.rank=rank;
    }
     @Override
        public int compareTo(Card other) {
            if(this.rank<other.rank) return -1;
            else if(other.rank< this.rank) return 1;
            return 0;
        }

}

score 2 · Answer 2 · edited May 23 '17 at 12:19

One of the overloads for Collections.max() takes a comparator as a second parameter. Using this you can implement your own comparator class like this:

class ValueComparator implements Comparator<Card> {
    @Override
    public int compare(Card a, Card b)
    {
        return a.rank > b.rank ? 1 : a.rank == b.rank ? 0 : -1;
    }
}

Then you can call max with:

Card maximum = Collections.max(trick, new ValueComparator());

The value of doing it this way is that you can create multiple comparators and use them to do comparison-based operations(max, sort, etc...) for a variety of comparison types. For example if you wanted to compare on the suit of the card you could implement a suit comparator. This Question and its answers provide some very helpful examples of how to use comparators.

score 1 · Answer 3 · edited Jan 18 '16 at 20:53

1

It depends type of data the Java arrays are indexed by int. The maximum positive int in Java is 2^31 – 1 = 2,147,483,647. And the platform-specific limits can be really close to this number – for example 64bit MB Pro on Java 1.7 I can happily initialize arrays with up to 2,147,483,645 or Integer. MAX_VALUE-2 elements.

I think this is not a good practice. But it is a good information!

edited Jan 18 '16 at 20:53

Tejus Prasad

6,322
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answered Jan 18 '16 at 20:41

omairysdev

11
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Maximum value in array containing Objects Java

3 Answers3