code: public void beginDataSwapPhase(int numOfNewEntries){
  
          if (nextMap != null) {
              throw new IllegalStateException("Cannot call PhasedHeapFriendlyHashMap.beginDataSwapPhase(int), already in data swap phase");
          }
  
          recycler.swapCycleObjectArrays();
  
          nextMap = new HeapFriendlyHashMap<K, V>(numOfNewEntries, recycler);
      }
docs: Enters data swap phase<p />
  
  While in data swap phase, {@link PhasedHeapFriendlyHashMap#put(Object, Object)} can be used<p />
  
  @param numOfNewEntries Number of new entries expected to be added during the the data swap phase