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How to parameterize a comparable interface?

I have a main class - Simulator - which uses two other classes - Producer and Appraiser . The producer produces the results, and the Appraiser evaluates these results. The simulator controls the flow of work, requesting the Producer, and then passes the results to the Evaluator.

The actual implementation of the Producer and Appraiser is known at runtime, at compile time I only know their interfaces. Below I insert the contents of the interfaces, implementation examples, and the Simulator class.

Old code

package com.test;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

/**
 * Producers produce results. I do not care what is their type, but the values
 * in the map have to be comparable amongst themselves.
 */
interface IProducer {
    public Map<Integer, Comparable> getResults();
}

/**
 * This implementation ranks items in the map by using Strings.
 */
class ProducerA implements IProducer {
    @Override
    public Map<Integer, Comparable> getResults() {
        Map<Integer, Comparable> result = new HashMap<Integer, Comparable>();
        result.put(1, "A");
        result.put(2, "B");
        result.put(3, "B");
        return result;
    }
}

/**
 * This implementation ranks items in the map by using integers.
 */
class ProducerB implements IProducer {
    @Override
    public Map<Integer, Comparable> getResults() {
        Map<Integer, Comparable> result = new HashMap<Integer, Comparable>();
        result.put(1, 10);
        result.put(2, 30);
        result.put(3, 30);

        return result;
    }
}

/**
 * Evaluator evaluates the results against the given groundTruth. All it needs
 * to know about results, is that they are comparable amongst themselves.
 */
interface IEvaluator {
    public double evaluate(Map<Integer, Comparable> results,
            Map<Integer, Double> groundTruth);
}

/**
 * This is example of an evaluator (a metric) -- Kendall Tau B.
 */
class KendallTauB implements IEvaluator {
    @Override
    public double evaluate(Map<Integer, Comparable> results,
            Map<Integer, Double> groundTruth) {

        int concordant = 0, discordant = 0, tiedRanks = 0, tiedCapabilities = 0;

        for (Entry<Integer, Comparable> rank1 : results.entrySet()) {
            for (Entry<Integer, Comparable> rank2 : results.entrySet()) {
                if (rank1.getKey() < rank2.getKey()) {
                    final Comparable r1 = rank1.getValue();
                    final Comparable r2 = rank2.getValue();
                    final Double c1 = groundTruth.get(rank1.getKey());
                    final Double c2 = groundTruth.get(rank2.getKey());

                    final int rankDiff = r1.compareTo(r2);
                    final int capDiff = c1.compareTo(c2);

                    if (rankDiff * capDiff > 0) {
                        concordant++;
                    } else if (rankDiff * capDiff < 0) {
                        discordant++;
                    } else {
                        if (rankDiff == 0)
                            tiedRanks++;

                        if (capDiff == 0)
                            tiedCapabilities++;
                    }
                }
            }
        }

        final double n = results.size() * (results.size() - 1d) / 2d;

        return (concordant - discordant)
                / Math.sqrt((n - tiedRanks) * (n - tiedCapabilities));
    }
}

/**
 * The simulator class that queries the producer and them conveys results to the
 * evaluator.
 */
public class Simulator {
    public static void main(String[] args) {
        Map<Integer, Double> groundTruth = new HashMap<Integer, Double>();
        groundTruth.put(1, 1d);
        groundTruth.put(2, 2d);
        groundTruth.put(3, 3d);

        List<IProducer> producerImplementations = lookUpProducers();
        List<IEvaluator> evaluatorImplementations = lookUpEvaluators();

        IProducer producer = producerImplementations.get(1); // pick a producer
        IEvaluator evaluator = evaluatorImplementations.get(0); // pick an evaluator
        // Notice that this class should NOT know what actually comes from
        // producers (besides that is comparable)
        Map<Integer, Comparable> results = producer.getResults();
        double score = evaluator.evaluate(results, groundTruth);

        System.out.printf("Score is %.2f\n", score);
    }

    // Methods below are for demonstration purposes only. I'm actually using
    // ServiceLoader.load(Clazz) to dynamically discover and load classes that
    // implement these interfaces

    public static List<IProducer> lookUpProducers() {
        List<IProducer> producers = new ArrayList<IProducer>();
        producers.add(new ProducerA());
        producers.add(new ProducerB());

        return producers;
    }

    public static List<IEvaluator> lookUpEvaluators() {
        List<IEvaluator> evaluators = new ArrayList<IEvaluator>();
        evaluators.add(new KendallTauB());

        return evaluators;
    }
}

This code should compile and run. You should get the same result (0.82), regardless of which version of the manufacturer you choose.

, :

  • Simulator, IEvaluator IProducer, , IProducer, , Comparable: Comparable - raw. Comparable
  • , IEvaluator, ( compareTo() Map): : compareTo (Object) Comparable. Comparable

, , . . , , IEvaluator IProducer, IProducer IEvaluator.

:

  • , . , Comparable.
  • , IEvaluator , , , ( IEvaluator compareTo().)
  • Simulator "" - ( , , ). - .

?

, , SuppressWarnings. , , .

package com.test;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

/**
 * Producers produce results. I do not care what is their type, but the values
 * in the map have to be comparable amongst themselves.
 */
interface IProducer<T extends Comparable<T>> {
    public Map<Integer, T> getResults();
}

/**
 * This implementation ranks items in the map by using Strings.
 */
class ProducerA implements IProducer<String> {
    @Override
    public Map<Integer, String> getResults() {
        Map<Integer, String> result = new HashMap<Integer, String>();
        result.put(1, "A");
        result.put(2, "B");
        result.put(3, "B");

        return result;
    }
}

/**
 * This implementation ranks items in the map by using integers.
 */
class ProducerB implements IProducer<Integer> {
    @Override
    public Map<Integer, Integer> getResults() {
        Map<Integer, Integer> result = new HashMap<Integer, Integer>();
        result.put(1, 10);
        result.put(2, 30);
        result.put(3, 30);

        return result;
    }
}

/**
 * Evaluator evaluates the results against the given groundTruth. All it needs
 * to know about results, is that they are comparable amongst themselves.
 */
interface IEvaluator {
    public <T extends Comparable<T>> double evaluate(Map<Integer, T> results,
            Map<Integer, Double> groundTruth);
}

/**
 * This is example of an evaluator (a metric) -- Kendall Tau B.
 */
class KendallTauB implements IEvaluator {
    @Override
    public <T extends Comparable<T>> double evaluate(Map<Integer, T> results,
            Map<Integer, Double> groundTruth) {
        int concordant = 0, discordant = 0, tiedRanks = 0, tiedCapabilities = 0;

        for (Entry<Integer, T> rank1 : results.entrySet()) {
            for (Entry<Integer, T> rank2 : results.entrySet()) {
                if (rank1.getKey() < rank2.getKey()) {
                    final T r1 = rank1.getValue();
                    final T r2 = rank2.getValue();
                    final Double c1 = groundTruth.get(rank1.getKey());
                    final Double c2 = groundTruth.get(rank2.getKey());

                    final int rankDiff = r1.compareTo(r2);
                    final int capDiff = c1.compareTo(c2);

                    if (rankDiff * capDiff > 0) {
                        concordant++;
                    } else if (rankDiff * capDiff < 0) {
                        discordant++;
                    } else {
                        if (rankDiff == 0)
                            tiedRanks++;

                        if (capDiff == 0)
                            tiedCapabilities++;
                    }
                }
            }
        }

        final double n = results.size() * (results.size() - 1d) / 2d;

        return (concordant - discordant)
                / Math.sqrt((n - tiedRanks) * (n - tiedCapabilities));
    }
}

/**
 * The simulator class that queries the producer and them conveys results to the
 * evaluator.
 */
public class Main {
    public static void main(String[] args) {
        Map<Integer, Double> groundTruth = new HashMap<Integer, Double>();
        groundTruth.put(1, 1d);
        groundTruth.put(2, 2d);
        groundTruth.put(3, 3d);

        List<IProducer<?>> producerImplementations = lookUpProducers();
        List<IEvaluator> evaluatorImplementations = lookUpEvaluators();

        IProducer<?> producer = producerImplementations.get(0);
        IEvaluator evaluator = evaluatorImplementations.get(0);

        // Notice that this class should NOT know what actually comes from
        // producers (besides that is comparable)
        double score = evaluator.evaluate(producer.getResults(), groundTruth);

        System.out.printf("Score is %.2f\n", score);
    }

    // Methods below are for demonstration purposes only. I'm actually using
    // ServiceLoader.load(Clazz) to dynamically discover and load classes that
    // implement these interfaces
    public static List<IProducer<?>> lookUpProducers() {
        List<IProducer<?>> producers = new ArrayList<IProducer<?>>();
        producers.add(new ProducerA());
        producers.add(new ProducerB());

        return producers;
    }

    public static List<IEvaluator> lookUpEvaluators() {
        List<IEvaluator> evaluators = new ArrayList<IEvaluator>();
        evaluators.add(new KendallTauB());

        return evaluators;
    }
}

, -, , .

    public static void main(String[] args) {
        Map<Integer, Double> groundTruth = new HashMap<Integer, Double>();
        groundTruth.put(1, 1d);
        groundTruth.put(2, 2d);
        groundTruth.put(3, 3d);

        List<IProducer<?>> producerImplementations = lookUpProducers();
        List<IEvaluator> evaluatorImplementations = lookUpEvaluators();

        IProducer<?> producer = producerImplementations.get(0);
        IEvaluator evaluator = evaluatorImplementations.get(0);

        // Notice that this class should NOT know what actually comes from
        // producers (besides that is comparable)
        double score = evaluator.evaluate(producer.getResults(), groundTruth);

        System.out.printf("Score is %.2f\n", score);
    }

. , :

    public static void main(String[] args) {
        Map<Integer, Double> groundTruth = new HashMap<Integer, Double>();
        groundTruth.put(1, 1d);
        groundTruth.put(2, 2d);
        groundTruth.put(3, 3d);

        List<IProducer<?>> producerImplementations = lookUpProducers();
        List<IEvaluator> evaluatorImplementations = lookUpEvaluators();

        IProducer<?> producer = producerImplementations.get(0);
        IEvaluator evaluator = evaluatorImplementations.get(0);

        // Notice that this class should NOT know what actually comes from
        // producers (besides that is comparable)

        // Lines below changed
        Map<Integer, ? extends Comparable<?>> ranks = producer.getResults();            
        double score = evaluator.evaluate(ranks, groundTruth);

        System.out.printf("Score is %.2f\n", score);
}

, : : (Map, Map) IEvaluator (Map > Map). # 3-of? extends Comparable a >

. , .evaluate(manufacturer.getResults(), groundTruth). , .getResults() , ( .evaluate(ranks, groundTruth)), ( ).

+5
3

. :

  • , ,
  • , ,
  • , , .

:

package com.test;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

/**
 * Producers produce results. I do not care what their actual type is, but the
 * values in the map have to be comparable amongst themselves.
 */
interface IProducer<T extends Comparable<T>> {
    public Map<Integer, T> getResults();
}

/**
 * This example implementation ranks items in the map by using Strings.
 */
class ProducerA implements IProducer<String> {
    @Override
    public Map<Integer, String> getResults() {
        Map<Integer, String> result = new HashMap<Integer, String>();
        result.put(1, "A");
        result.put(2, "B");
        result.put(3, "B");

        return result;
    }
}

/**
 * This example implementation ranks items in the map by using integers.
 */
class ProducerB implements IProducer<Integer> {
    @Override
    public Map<Integer, Integer> getResults() {
        Map<Integer, Integer> result = new HashMap<Integer, Integer>();
        result.put(1, 10);
        result.put(2, 30);
        result.put(3, 30);

        return result;
    }
}

/**
 * Evaluator evaluates the results against the given groundTruth. All it needs
 * to know about results, is that they are comparable amongst themselves.
 */
interface IEvaluator {
    public <T extends Comparable<T>> double evaluate(Map<Integer, T> results,
            Map<Integer, Double> groundTruth);
}

/**
 * This is example of an evaluator, metric Kendall Tau-B. Don't bother with
 * semantics, all that matters is that I want to be able to call
 * r1.compareTo(r2) for every (r1, r2) that appear in Map<Integer, T> results.
 */
class KendallTauB implements IEvaluator {
    @Override
    public <T extends Comparable<T>> double evaluate(Map<Integer, T> results,
            Map<Integer, Double> groundTruth) {
        int concordant = 0, discordant = 0, tiedRanks = 0, tiedCapabilities = 0;

        for (Entry<Integer, T> rank1 : results.entrySet()) {
            for (Entry<Integer, T> rank2 : results.entrySet()) {
                if (rank1.getKey() < rank2.getKey()) {
                    final T r1 = rank1.getValue();
                    final T r2 = rank2.getValue();
                    final Double c1 = groundTruth.get(rank1.getKey());
                    final Double c2 = groundTruth.get(rank2.getKey());

                    final int ranksDiff = r1.compareTo(r2);
                    final int actualDiff = c1.compareTo(c2);

                    if (ranksDiff * actualDiff > 0) {
                        concordant++;
                    } else if (ranksDiff * actualDiff < 0) {
                        discordant++;
                    } else {
                        if (ranksDiff == 0)
                            tiedRanks++;

                        if (actualDiff == 0)
                            tiedCapabilities++;
                    }
                }
            }
        }

        final double n = results.size() * (results.size() - 1d) / 2d;

        return (concordant - discordant)
                / Math.sqrt((n - tiedRanks) * (n - tiedCapabilities));
    }
}

/**
 * The simulator class that queries the producer and them conveys results to the
 * evaluator.
 */
public class Simulator {
    public static void main(String[] args) {
        // example of a ground truth
        Map<Integer, Double> groundTruth = new HashMap<Integer, Double>();
        groundTruth.put(1, 1d);
        groundTruth.put(2, 2d);
        groundTruth.put(3, 3d);

        // dynamically load producers
        List<IProducer<?>> producerImplementations = lookUpProducers();

        // dynamically load evaluators
        List<IEvaluator> evaluatorImplementations = lookUpEvaluators();

        // pick a producer
        IProducer<?> producer = producerImplementations.get(0);

        // pick an evaluator
        IEvaluator evaluator = evaluatorImplementations.get(0);

        // evaluate the result against the ground truth
        double score = evaluator.evaluate(producer.getResults(), groundTruth);

        System.out.printf("Score is %.2f\n", score);
    }

    // Methods below are for demonstration purposes only. I'm actually using
    // ServiceLoader.load(Clazz) to dynamically discover and load classes that
    // implement interfaces IProducer and IEvaluator
    public static List<IProducer<?>> lookUpProducers() {
        List<IProducer<?>> producers = new ArrayList<IProducer<?>>();
        producers.add(new ProducerA());
        producers.add(new ProducerB());

        return producers;
    }

    public static List<IEvaluator> lookUpEvaluators() {
        List<IEvaluator> evaluators = new ArrayList<IEvaluator>();
        evaluators.add(new KendallTauB());

        return evaluators;
    }
}
+1

, . - :

import java.util.Map;
import java.util.HashMap;

interface IProducer<T extends Comparable<? super T>> {
    public Map<Integer, T> getResults();
}

interface IEvaluator {
    public <T extends Comparable<? super T>> double evaluate(Map<Integer, T> results,
                                                             Map<Integer, Double> groundTruth);
}

public class Main {
  public static void main(String[] args) {
    IProducer<String> producer = null;
    IEvaluator evaluator = null;
    Map<Integer, String> results = producer.getResults();
    double score = evaluator.evaluate(results, new HashMap<Integer, Double>());
  }
}
+2

- ?

public interface IProducer<T extends Comparable<? super T>> {
    public Map<Integer, T> getResults();
}

Whenever I implement Comparable (or extend Comparator), I always do something like this:

public class Dog implements Comparable<Dog> {

    private String breed;

    public String getBreed() {
        return breed;
    }

    public void setBreed(String s) {
        breed = s;
    }

    public int compareTo(Dog d) {
        return breed.compareTo(d.getBreed());
    }

}

Note that there is no need to use the object in compareTo when setting Comparable.

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