ADDITIONAL SYSTEM INFORMATION :
Found this error with antique tomcat 4 and jdk1.8.0_111
Upgraded to tomcat 9 and jdk-12.0.2
Same error.


A DESCRIPTION OF THE PROBLEM :
This bug does NOT occur in
winxp
     jdk1.6.0_21
It DOES occur in
win7
     jdk1.8.0_111
     jdk-12.0.2

The problem is in timsort that fails to sort a Vector with 143
elements that are comparable.
Here a trace fragment from deep down a tomcat web server:

 java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.base/java.util.ComparableTimSort.mergeLo(ComparableTimSort.java:748)
at java.base/java.util.ComparableTimSort.mergeAt(ComparableTimSort.java:485)
at java.base/java.util.ComparableTimSort.mergeForceCollapse(ComparableTimSort.java:426)
at java.base/java.util.ComparableTimSort.sort(ComparableTimSort.java:222)
at java.base/java.util.Arrays.sort(Arrays.java:1316)
at java.base/java.util.Arrays.sort(Arrays.java:1510)
at java.base/java.util.Vector.sort(Vector.java:1412)
at java.base/java.util.Collections.sort(Collections.java:145)
at edit.Simulation.foo(Simulation.java:474)

Replacing:
       Collections.sort(diseases);
by an ad hoc insertion sorter:
       sortd(diseases); // replacement
fixes this bug.
[ the insertion sorter:
    static Vector sortd(Vector<DiseaseInst> di) {
// simple insertionsort
int s = di.size();
if ( s <= 1 ) return di;
for ( int i = 1; i < s; i++ ) sortd1(di, i);
return di;
    } // end sortd
    static void sortd1(Vector<DiseaseInst> di, int i) {
DiseaseInst dii = di.elementAt(i);
for ( int j = i - 1; 0 <= j; j-- ) {
DiseaseInst dij = di.elementAt(j);
if ( dij.compareTo(dii) <= 0 ) {
di.set(j+1, dii);
return;
} else di.set(j+1, dij);
}
di.set(0, dii);
    } // end sortd1
]
Here the comparator of DiseaseInst:
  public int compareTo(Object o) {
    int i = inSymptoms.size();
    float rate = rate();
    DiseaseInst di2 = this;
    try { di2 = (DiseaseInst) o; } catch (ClassCastException ignore) {}
    float acceptanceRate2 = di2.getAcceptanceRate();
    int i2 = di2.getInSymptoms().size();
    float rate2 = di2.rate();

    if ( i == i2 ) {
if ( acceptanceRate2 < acceptanceRate ) return 1;
if ( acceptanceRate < acceptanceRate2 ) return -1;
if ( rate2 < rate ) return -1;
if ( rate < rate2 ) return 1;
return 0;
    }
    if ( rate2 < rate ) return -1;
    if ( rate < rate2 ) return 1;
    // rate == rate2
    if ( i2 < i ) return -1;
    if ( i < i2 ) return 1;
    if ( acceptanceRate2 < acceptanceRate ) return -1;
    if ( acceptanceRate < acceptanceRate2 ) return 1;
    return 0;
  } // end compareTo




STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Sorry/ I have spend two days on this error that happens in a 5mb servlet source.
I am not able to recode this stuff.
The trace may help you ...
[[ I do remember that this is the 2nd time there is a problem with timsort ]]


ACTUAL -
See the trace

---------- BEGIN SOURCE ----------
sorry ...
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
See above ... but that works only for small arrays ...

FREQUENCY : always