java 比较方法抛出异常：比较方法违反了它的一般约定
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/10234038/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Compare method throw exception: Comparison method violates its general contract
提问by famedoro
Possible Duplicate:
why does my compare method throw exception — Comparison method violates its general contract!
I've this code:
我有这个代码：
class TimeComparatorTipo0 implements Comparator {
@Override
public int compare(Object a, Object b) {
String Time1 = ((DataImportedTipo0) a).ora;
Long VolTot1 = Long.parseLong(((DataImportedTipo0) a).volume_totale);
String Time2 = ((DataImportedTipo0) b).ora;
Long VolTot2 = Long.parseLong(((DataImportedTipo0) b).volume_totale);
if (Time1.equals(Time2))
{
if ( VolTot1.compareTo(VolTot2) > 0)
return 1;
else
return -1;
}
else
return Time1.compareTo(Time2);
}
};
Sometimes it thrown this exception:
有时它抛出这个异常：
java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.util.TimSort.mergeHi(TimSort.java:868)
at java.util.TimSort.mergeAt(TimSort.java:485)
at java.util.TimSort.mergeForceCollapse(TimSort.java:426)
at java.util.TimSort.sort(TimSort.java:223)
at java.util.TimSort.sort(TimSort.java:173)
at java.util.Arrays.sort(Arrays.java:659)
at java.util.Collections.sort(Collections.java:217)
at ManageUrl.DownloadUrl.StartThreadDowloadTipo0(DownloadUrl.java:893)
at ManageUrl.DownloadUpdateWorkflow$ConsumerTipo0.run(DownloadUpdateWorkflow.java:278)
Why ?
为什么 ？
1) how can I avoid it? 2) how can i catch this exception ?
1）我怎样才能避免它？2）我怎样才能捕捉到这个异常？
Thanks in advance.
提前致谢。
回答by Peter Lawrey
If you have two elements when are equal aand byou will get compare(a, b) == -1and compare(b, a) == -1which doesn't make any sense.
如果你有两个相等的元素a，b你会得到compare(a, b) == -1和compare(b, a) == -1这没有任何意义。
You can simplify the code with and make it more efficient with
您可以简化代码并提高效率
class TimeComparatorTipo0 implements Comparator<DataImportedTipo0> {
@Override
public int compare(DataImportedTipo0 a, DataImportedTipo0 b) {
String Time1 = a.ora, Time2 = b.ora;
int cmp = Time1.compareTo(Time2);
if (cmp == 0) {
// avoid expensive operations.
Long VolTot1 = Long.parseLong(a.volume_totale);
Long VolTot2 = Long.parseLong(b.volume_totale);
cmp = VolTot1.compareTo(VolTot2);
}
return cmp;
