java.lang.IllegalArgumentException：比较方法违反其一般合同 [英] java.lang.IllegalArgumentException: Comparison method violates its general contract

问题描述

以下是我的比较器的比较方法。我不知道是什么问题。我查找了其他类似的标题问题和答案堆栈溢出，但不知道什么是我的方法，但我不断得到java.lang.IllegalArgumentException：比较方法违反了它的一般合同！

Hi below is my compare method of my comparator. I am not sure what is wrong. I looked up other similar titled questions and answers on stack overflow but not sure what is wrong with my method but I keep getting java.lang.IllegalArgumentException: Comparison method violates its general contract!

任何帮助将非常感谢。

public int compare(Node o1, Node o2)
{
    HashMap<Integer,Integer> childMap = orderMap.get(parentID);
    if(childMap != null && childMap.containsKey(o1.getID()) && 
                           childMap.containsKey(o2.getID()))
    {
        int order1 = childMap.get(o1.getID());
        int order2 = childMap.get(o2.getID());

        if(order1<order2) 
            return -1;
        else if(order1>order2) 
            return 1;
        else 
            return 0;
    }
    else
        return 0;
}

添加异常

java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.util.TimSort.mergeLo(TimSort.java:747)
at java.util.TimSort.mergeAt(TimSort.java:483)
at java.util.TimSort.mergeCollapse(TimSort.java:410)
at java.util.TimSort.sort(TimSort.java:214)
at java.util.TimSort.sort(TimSort.java:173)
at java.util.Arrays.sort(Arrays.java:659)
at java.util.Collections.sort(Collections.java:217)

推荐答案

您的 compare（）方法 / em> 。如果 A == B 和 B == C ，则 A 必须等于 C 。

Your compare() method is not transitive. If A == B and B == C, then A must be equal to C.

现在考虑这种情况：

A ， B 和 C ，假设 containsKey（）方法返回以下结果：

For A, B, and C, suppose the containsKey() method return these results:

• childMap.containsKey（A.getID（））返回 true


• childMap.containsKey（B.getID（））返回 false


• childMap.containsKey（C.getID（））返回 true

• childMap.containsKey(A.getID()) returns true
• childMap.containsKey(B.getID()) returns false
• childMap.containsKey(C.getID()) returns true

此外，考虑订单 A.getId（）！= B.getId（）

Also, consider orders for A.getId() != B.getId().

因此，

1. A 和会返回 0 ，如 if 条件将 false => A == B


2. code> B 和 C 会返回 0 $ c> if 条件将为 false => B == C

1. A and B would return 0, as outer if condition will be false => A == B
2. B and C would return 0, as outer if condition will be false => B == C

但是， A 和 C ，可以返回 -1 或 1 / code>块。所以， A！= C 。这违反了传递性原则。

But, A and C, could return -1, or 1, based on your test inside the if block. So, A != C. This violates the transitivity principle.

我想你应该在 else 块中添加一些条件， 如果阻止。

I think, you should add some condition inside your else block, that performs check similar to how you do in if block.

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