question: protected void addCounters ( BasicCounters < MutableLong > target , BasicCounters < MutableLong > source ) { for ( Enum < ReaderCounterKeys > key : ReaderCounterKeys . values ( ) ) { MutableLong tcounter = target . getCounter ( key ) ; if ( tcounter == null ) { tcounter = new MutableLong ( ) ; target . setCounter ( key , tcounter ) ; } MutableLong scounter = source . getCounter ( key ) ; if ( scounter != null ) { tcounter . add ( scounter . longValue ( ) ) ; } } }
target:  Transfers the counters in partitioning.