Java错误：“比较方法违反了其一般合同！” [英] Java error: "Comparison method violates its general contract!"

问题描述

我有这段代码：

package org.optimization.geneticAlgorithm;
import org.optimization.geneticAlgorithm.selection.Pair;

public abstract class Chromosome implements Comparable<Chromosome> {
    public abstract double fitness();
    public abstract Pair<Chromosome> crossover(Chromosome parent);
    public abstract void mutation();
    public int compareTo(Chromosome o) {
        int rv = 0;
        if (this.fitness() > o.fitness()) {
            rv = -1;
        } else if (this.fitness() < o.fitness()) {
            rv = 1;
        }
        return rv;
    }
}

每次运行此代码时都会出现此错误：

And every time I run this code I get this error:

Exception in thread "main" java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.util.ComparableTimSort.mergeHi(ComparableTimSort.java:835)
at java.util.ComparableTimSort.mergeAt(ComparableTimSort.java:453)
at java.util.ComparableTimSort.mergeCollapse(ComparableTimSort.java:376)
at java.util.ComparableTimSort.sort(ComparableTimSort.java:182)
at java.util.ComparableTimSort.sort(ComparableTimSort.java:146)
at java.util.Arrays.sort(Arrays.java:472)
at java.util.Collections.sort(Collections.java:155)
at org.optimization.geneticAlgorithm.GeneticAlgorithm.nextGeneration(GeneticAlgorithm.java:74)
at org.optimization.geneticAlgorithm.GeneticAlgorithm.execute(GeneticAlgorithm.java:40)
at test.newData.InferenceModel.main(InferenceModel.java:134)

我使用OpenJDK7u3并在对象相等时返回0。有人可以向我解释这个错误吗？

I use OpenJDK7u3 and I return 0 when the objects are equal. Can someone explain this error to me?

推荐答案

如果您有任何NaN值，您可能会遇到这种情况：

You could get into that situation if you have any NaN values:

例如：

public class Test
{
    public static void main(String[] args) {
        double a = Double.NaN;
        double b = Double.NaN;
        double c = 5;

        System.out.println(a < b);
        System.out.println(a > b);
        System.out.println(b < c);
        System.out.println(c < b);
    }
}

这些打印的所有 假。所以你最终可能会遇到两个非NaN值都被认为与NaN相等的情况，但是一个比另一个更大。基本上，您应该弄清楚如何处理NaN值。还要检查那确实是问题，当然......你真的想要NaN值来适应你的身体吗？

All of these print false. So you could end up in a situation where two non-NaN values were both deemed "equal" to NaN, but one was greater than the other. Basically, you should work out how you want to handle NaN values. Also check that that really is the problem, of course... do you really want NaN values for your fitness?

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