A NonDecomposableAggregatorFunction must implement getFinalValue method.This method returns the final results at the end of each input partition. The final result should be in the type ValueHolder.
Below is an example of a simple function that counts the number of rows for each input partition. The getFinalValue method returns the final count as a long value.
// Return the final form of the count.
public ValueHolder getFinalValue() {
countValue_.setLong(count_);
return countValue_.clone();
}