如何参数化可比接口?

时间:2012-08-30 00:07:03

标签: java generics interface wildcard

我有一个主要类 - 模拟器 - 它使用另外两个类 - Producer Evaluator 。生产者生成结果,而评估者评估这些结果。模拟器通过查询生产者然后将结果传送给评估者来控制执行流程。

生产者和评估者的实际实现在运行时是已知的,在编译时我只知道他们的接口。下面我粘贴接口,示例实现和Simulator类的内容。

旧代码

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's 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;
    }
}

此代码应编译并运行。无论选择哪个生成器实现,都应该得到相同的结果(0.82)。

编译器警告我不要在几个地方使用泛型:

  • 在Simulator类中,在接口IEvaluator和IProducer中,以及在实现IProducer接口的类中,每当我引用Comparable接口时,都会收到以下警告: Comparable是一种原始类型。对泛型类型Comparable的引用应该参数化
  • 在实现IEvaluator的类中,我得到以下警告(当对Map的值调用compareTo()时):类型安全:方法compareTo(Object)属于原始类型Comparable。对泛型类型Comparable的引用应该参数化

所有这一切,模拟器工作。现在,我想摆脱编译警告。问题是,我不知道如何参数化IEkgator和IProducer接口,以及如何更改IProducer和IEvaluator的实现。

我有一些限制:

  • 我无法知道生产者将返回的地图中的值类型。但我知道,他们都将属于同一类型,并且他们将实现Comparable接口。
  • 类似地,IEvaluator实例不需要知道任何正在评估的结果,除了它们是相同的类型并且它们是可比较的(IEvaluator实现需要能够调用compareTo()方法。)。
  • 我必须让Simulator类不受这种“可比较”困境的影响 - 它不需要知道关于这些类型的任何信息(除了相同的类型,也可以比较)。它的工作是简单地将生产者的结果传递给评估者。

有什么想法吗?

编辑和修订版

使用下面答案中的一些想法,我进入了这个阶段,它编译并运行时没有警告,也不需要使用SuppressWarnings指令。这与Eero建议的非常相似,但主要方法略有不同。

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's 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;
    }
}

关键区别似乎在主要方法中,目前看起来像这样。

    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);
    }

这很有效。但是,如果我将代码更改为:

    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);
}

darn的东西甚至都不会编译,说:绑定不匹配:IEvaluator类型的泛型方法evaluate(Map,Map)不适用于参数(Map&gt;,Map)。推断类型捕获#3-of? extends Comparable不是有界参数&gt;

的有效替代品

这对我来说非常奇怪。如果我调用evaluateator.evaluate(producer.getResults(),groundTruth),代码就可以工作。但是,如果我首先调用producer.getResults()方法,并将其存储到变量中,然后使用该变量调用evaluate方法(evaluateator.evaluate(ranking,groundTruth)),我会得到编译错误(无论该变量是什么)类型)。

3 个答案:

答案 0 :(得分:2)

您需要指定对象愿意与之比较的内容。类似的东西:

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>());
  }
}

答案 1 :(得分:1)

我在下面发布了我的答案。一些说明:

  • 制作人显然知道自己的类型
  • 在调用方法之前,Evaluator不知道它正在处理什么
  • producerImplementations包含几种不同的类型,因此当您实际选择其中一种时,最终会有一个强制转换。

以下代码:

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;
    }
}

答案 2 :(得分:0)

警告是否只是要求你做这样的事情?

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

每当我实现 Comparable (或扩展 Comparator )时,我总是这样做:

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());
    }

}

请注意,当 Comparable 参数化时,无需在 compareTo 中使用对象。