Question

I have an ArrayList of ArrayList of Bean and I need to sort this ArrayList according to the date variable in Bean.

ArrayList<ArrayList<DriverLogDatePair>> driverLogList

And DriverLogDatePair bean have a variable DateTime date, it also has a compareTo method.

public int compareTo(DriverLogDatePair o) {
    return date.compareTo(o.date);
}

But I am not able to sort driverLogList.

Answer 1

You have to complete this code:

ArrayList<ArrayList<DriverLogDatePair>> driverLogList = new ArrayList<>();
Collections.sort( driverLogList, new Comparator<ArrayList<DriverLogDatePair>>(){
   @Override public int compare(
      ArrayList<DriverLogDatePair> left,
      ArrayList<DriverLogDatePair> right )
   {
      return 0;
   }});

Because the first array contains an array which contains a Comparable.
The comparator you provide is for DriverLogDatePair not for ArrayList< DriverLogDatePair >

(… After comments of this post… )

At your request, to complete the comparator I suggest:

int size = left.size();
int diff = size - right.size();
if( diff != 0 ) return diff;
for( int i = 0; i < size; ++i ) {
   diff = left.get( i ).compareTo( right.get(i) );
   if( diff != 0 ) return diff;
}

But I have no idea of the true meaning of this comparison.
It’s a semantic problem, is this really what you want?