java-7 - 比较方法违反了它的一般契约!仅限 Java 7

Question

我知道这个问题已经有一段时间了，并检查了我之前可以获得的所有答案，但这个仍然不起作用。

对象“crew”代表具有等级和其他项目的船员。应通过比较 int 值“assigned_rank”来进行比较，如果两个实例中该值相等，则 bool 值“is_trainer”应该会产生差异。

只要使用 java < 7 运行，此方法就非常有效。但自从 Java 7 以来，我一直得到这个:

java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.util.ComparableTimSort.mergeLo(ComparableTimSort.java:714)
at java.util.ComparableTimSort.mergeAt(ComparableTimSort.java:451)
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 dormas_flightlog.Query.getCrew(Query.java:714)

这是来源，其中一些潜在危险的部分已经被注释掉，但它仍然不起作用:

public class crew implements Serializable, Comparable<crew> {

private static final long serialVersionUID = 36L;
private int flightID = 0;
private int assigned_rank = 25;
private boolean is_trainer = false;
...


@Override
public int compareTo(crew him) {

    int myRank = this.getAssigned_rank();
    int hisRank = him.assigned_rank;

    if (this == him) {
        return 0;
    }
    if (myRank > hisRank) {
        return 1;
    }
    if (myRank < hisRank) {
        return -1;
    }
    if (myRank == hisRank) {
//            if (is_trainer && !o.is_trainer) {
//                i = 1;
//            }
//            if (!is_trainer && o.is_trainer) {
//                i = -1;
//            }
//            if (is_trainer && o.is_trainer) {
//                i = 0;
//            }
//            if (!is_trainer && !o.is_trainer) {
//                i = 0;
//            }
        return 0;
    }

    return 0;
}

@Override
public int hashCode() {
    int hash = 7;
    hash = 31 * hash + this.assigned_rank;
    hash = 31 * hash + (this.is_trainer ? 1 : 0);
    return hash;
}

@Override
public boolean equals(Object o) {

    if (this == o) {
        return true;
    }


    int myRank = this.getAssigned_rank();
    int hisRank = 0;

    if (o instanceof crew) {
        crew him = (crew) o;
        hisRank = him.assigned_rank;
    } else {
        return false;
    }

    if (myRank > hisRank) {
        return false;
    }
    if (myRank < hisRank) {
        return false;
    }
    if (myRank == hisRank) {
//            if (is_trainer && !o.is_trainer) {
//                i = 1;
//            }
//            if (!is_trainer && o.is_trainer) {
//                i = -1;
//            }
//            if (is_trainer && o.is_trainer) {
//                i = 0;
//            }
//            if (!is_trainer && !o.is_trainer) {
//                i = 0;
//            }
        return true;
    }

    return false;
}

}

实现 equals() 只是解决这个问题的尝试。给定的异常带有或不带有 equals()。我看不出compareTo 方法如何违反其契约。非常感谢任何帮助...有一天这段代码必须与 java 7 一起工作，但我不知道如何... 谢谢

Answer 1

看这个:

来自http://www.oracle.com/technetwork/java/javase/compatibility-417013.html#source

Area: API: Utilities Synopsis: Updated sort behavior for Arrays and Collections may throw an IllegalArgumentException

Description: The sorting algorithm used by java.util.Arrays.sort and (indirectly) by java.util.Collections.sort has been replaced. The new sort implementation may throw an IllegalArgumentException if it detects a Comparable that violates the Comparable contract. The previous implementation silently ignored such a situation. If the previous behavior is desired, you can use the new system property java.util.Arrays.useLegacyMergeSort, to restore previous mergesort behavior.

Nature of Incompatibility: behavioral

RFE: 6804124

有关更多详细信息，请参阅错误数据库 reference here .