Java错误：“比较方法违反了其一般约定！”

Question

我有以下代码：

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;
    }
}

每次我运行此代码时，都会出现此错误：

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，当对象相等时返回0。有人可以向我解释这个错误吗？

Answer 1

如果您有任何NaN值，则可能会遇到这种情况：

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);
    }
}

所有
这些打印false。因此，您可能会遇到以下两种情况：两个非NaN值都被认为与NaN“相等”，但是一个大于另一个。基本上，您应该弄清楚如何处理NaN值。当然，还要检查这确实是问题所在……您是否真的想要适合自己的NaN值？