我在网上尝试了许多可能的解决方案,比如设置System属性并转换为double但仍然得到相同的错误:
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.mergeForceCollapse(ComparableTimSort.java:392)
at java.util.ComparableTimSort.sort(ComparableTimSort.java:191)
at java.util.ComparableTimSort.sort(ComparableTimSort.java:146)
at java.util.Arrays.sort(Arrays.java:472)
at java.util.Collections.sort(Collections.java:155)
这是我的代码:
System.setProperty("java.util.Arrays.useLegacyMergeSort", "true");
Collections.sort(docs, new Comparator<FeedDocument>() {
public int compare(FeedDocument o1, FeedDocument o2) {
int year1 = 0;
int year2 = 0;
int returnResult = 0;
if (o1.containsKey(FeedConstants.PUBLICATION_YEAR)
&& o2.containsKey(FeedConstants.PUBLICATION_YEAR)
&& o1.get(FeedConstants.PUBLICATION_YEAR) != null
&& (o1.get(FeedConstants.PUBLICATION_YEAR) instanceof String)
&& o2.get(FeedConstants.PUBLICATION_YEAR) != null
&& (o2.get(FeedConstants.PUBLICATION_YEAR) instanceof String)) {
String firstyear = (String) o1.get((FeedConstants.PUBLICATION_YEAR));
String secondyear = (String) o2.get((FeedConstants.PUBLICATION_YEAR));
if (firstyear.equals(secondyear)) {
return 0;
} else if (firstyear != null && !firstyear.isEmpty() && secondyear != null
&& !secondyear.isEmpty()) {
year1 = Integer.parseInt(firstyear.trim());
year2 = Integer.parseInt(secondyear.trim());
// int result = year2 - year1;
// if (result > 0) {
// returnResult = 1;
// } else if (result < 0) {
// returnResult = -1;
// }
return Double.compare(year2, year1);
}
} else {
returnResult = 0;
}
return returnResult;
}
});
答案 0 :(得分:4)
很确定我知道这里发生了什么......
补充:
o1.get(FeedConstants.PUBLICATION_YEAR) != null
o2.get(FeedConstants.PUBLICATION_YEAR) == null
o3.get(FeedConstants.PUBLICATION_YEAR) != null
然后:
compare (o1, o2); //returns 0
compare (o2, o3); //returns 0
compare (o1, o3); //returns not 0
因此,您声明o1 == o2 == o3
但o1 != o3
答案 1 :(得分:0)
Edward Peters' answer在诊断问题时是正确的,因为compare
方法不会产生一致(传递)结果。
解决此问题的最佳方法类似于compare
方法中的以下内容:
if (o1.get(FeedConstants.PUBLICATION_YEAR) instanceof String) {
if (o2.get(FeedConstants.PUBLICATION_YEAR) instanceof String) {
// Perform the comparison here like you are
} else {
/*
* This could also be 1, the key is to have it consistent
* so the final sorted list clearly separates the FeedDocuments
* with a String PUBLICATION_YEAR and those without one.
*/
return -1;
}
} else if (o2.get(FeedConstants.PUBLICATION_YEAR) instanceof String) {
/*
* In this case, o1 doesn't have a String PUBLICATION_YEAR and o2
* does, so this needs to be the opposite of the return value
* 6 lines up to be consistent.
*/
return 1;
} else {
/*
* Consider all FeedDocuments without a String PUBLICATION_YEAR
* to be equivalent, otherwise you could do some other comparison
* on them here if you wanted.
*/
return 0;
}
关键是,如果您只关心正在排序的列表的子集(FeedDocument
的{{1}}出版年份,那么您需要先将它们与列表的其余部分分开您不关心被排序(当String
中的一个有FeedDocument
出版年份而另一个没有时,返回1或-1。然后,您可以自由地对所需的子集进行排序,但结果不一致。