user3422177:

Exception in thread "main" java.lang.IllegalArgumentException: 
Comparison method violates its general contract!
    at java.util.ComparableTimSort.mergeLo(ComparableTimSort.java:744)
    at java.util.ComparableTimSort.mergeAt(ComparableTimSort.java:481)
    at java.util.ComparableTimSort.mergeCollapse(ComparableTimSort.java:406)
    at java.util.ComparableTimSort.sort(ComparableTimSort.java:213)
    at java.util.Arrays.sort(Arrays.java:1246)
    at Solution.main(Solution.java:16)

This is the exception when I am running my program. Error occurs when I am using Arrays.sort function on an array of objects of class Element described as

static class Element implements Comparable{
    int pos,val;
    Element(int pos,int val){
        this.pos=pos;
        this.val=val;
    }
    public int compareTo(Element a){
        if(val!=a.val)
            return val-a.val;
        return pos-a.pos;
    }
}

It runs perfectly fine in some cases but throws the above error in other cases. What is the error in my program?