Question

I got hit with the (apparently infamous) IllegalArgumentException using Collections.sort() in Java7
Thanks to SO I understand the cause, which is basically (cough) poor code.
The thing is, I cannot reproduce the Exception myself. I did some jdk source code digging, and located which class is throwing that exception. The idea is to create the according Test Case.

Here is the code, by the way
< pride level=”0″ >

@Override
public int compareTo( Symbol other) {
    if( this.lastUse == 0) {
        if( other.lastUse != 0) return (int)( -DateMicros.ONE_DAY);
    } else if( other.lastUse == 0) {
        return ( int)DateMicros.ONE_DAY;
    }
    return ( int)( this.lastUse - other.lastUse);
}

< /pride >
On top of this, “lastUse” gets assigned timestamps in microseconds and milliseconds (yes mixed) which gives a superb int overflow spillage

The actual question is:
What Values Would make This Code Crash? to get a proper test case down the road.

Update with stack trace:

at java.util.ComparableTimSort.mergeHi(Unknown Source)
at java.util.ComparableTimSort.mergeAt(Unknown Source)
at java.util.ComparableTimSort.mergeCollapse(Unknown Source)
at java.util.ComparableTimSort.sort(Unknown Source)
at java.util.ComparableTimSort.sort(Unknown Source)
at java.util.Arrays.sort(Unknown Source)
at java.util.Collections.sort(Unknown Source)

Answer 1

Hard to tell without looking at the stacktrace itself.

But the docs mentions that the method itself can throw the exception.

(optional) if the implementation detects that the natural ordering of the list elements is found to violate the Comparable contract

Update

It looks like because your object does not fulfull the Comparable consistency requirement:

The natural ordering for a class C is said to be consistent with equals if and only if e1.compareTo(e2) == 0 has the same boolean value as e1.equals(e2) for every e1 and e2 of class C. Note that null is not an instance of any class, and e.compareTo(null) should throw a NullPointerException even though e.equals(null) returns false.