I agree in theory. But in practice that specific caller's code bug was so widespread and Timsort broke so much existing code that it warranted offering a "-Djava.util.Arrays.useLegacyMergeSort=true" option.
The specific line from the Javadoc you're alluding to [0] is:
> The implementor must ensure sgn(x.compareTo(y)) == -sgn(y.compareTo(x)) for all x and y.
The problem is the second implied half of that statement: Pre-Timsort it was ", and if you don't, results might not be sorted in the correct order" while with Timsort it was ", and if you don't, you will get a RuntimeException."
It's way too easy to accidentally violate that condition: System.currentTimeMillis(), incorrect null handling, random numbers. Sometimes not even in the Comparator itself. The condition I posted, plus the other two:
> The implementor must also ensure that the relation is transitive: (x.compareTo(y)>0 && y.compareTo(z)>0) implies x.compareTo(z)>0.
> Finally, the implementor must ensure that x.compareTo(y)==0 implies that sgn(x.compareTo(z)) == sgn(y.compareTo(z)), for all z.
Are just way too easy for someone to inadvertently violate to justify a RuntimeException when it occurs.
[0] https://docs.oracle.com/javase/7/docs/api/java/lang/Comparab...
The specific line from the Javadoc you're alluding to [0] is:
> The implementor must ensure sgn(x.compareTo(y)) == -sgn(y.compareTo(x)) for all x and y.
The problem is the second implied half of that statement: Pre-Timsort it was ", and if you don't, results might not be sorted in the correct order" while with Timsort it was ", and if you don't, you will get a RuntimeException."
It's way too easy to accidentally violate that condition: System.currentTimeMillis(), incorrect null handling, random numbers. Sometimes not even in the Comparator itself. The condition I posted, plus the other two:
> The implementor must also ensure that the relation is transitive: (x.compareTo(y)>0 && y.compareTo(z)>0) implies x.compareTo(z)>0.
> Finally, the implementor must ensure that x.compareTo(y)==0 implies that sgn(x.compareTo(z)) == sgn(y.compareTo(z)), for all z.
Are just way too easy for someone to inadvertently violate to justify a RuntimeException when it occurs.
[0] https://docs.oracle.com/javase/7/docs/api/java/lang/Comparab...