code: public void handleContextVector(String focusKey,
                                      String secondaryKey,
                                      SparseDoubleVector context) {
          // Get the list of context vectors for the focus key.
          List<SparseDoubleVector> termContexts = dataVectors.get(focusKey);
          if (termContexts == null) {
              synchronized (this) {
                  termContexts = dataVectors.get(focusKey);
                  if (termContexts == null) {
                      termContexts = new ArrayList<SparseDoubleVector>();
                      dataVectors.put(focusKey, termContexts);
                  }
              }
          }
  
          // Add the new context vector.
          int contextId = 0;
          synchronized (termContexts) {
              contextId = termContexts.size();
              termContexts.add(context);
          }
  
          // Record the association.
          if (reporter != null)
              reporter.assignContextToKey(focusKey, secondaryKey, contextId);
      }
docs: Adds the context vector to the end of the list of context vectors
  associated with {@code focusKey}.