java中排序报：Comparison method violates its general contract异常的解决

前言

上周线上的一段排序的java代码出现了一个Comparison method violates its general contract，在解决这个问题的途中学到了一些知识这里总结分享一下。

异常原因

这个排序导致的异常将会在java7以上的版本出现，所以如果你的jdk从6升级到了7或者8，那一定要小心此异常。

在java7的兼容列表中，就有对此排序不兼容的说明：

Area: api: UtilitiesSynopsis: Updated sort behavior for Arrays and Collections may throw an IllegalArgumentExceptionDescription: 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: behavioralRFE: 6804124