public void enqueueOperation(final String key, final Operation o) {
    checkState();
    StringUtils.validateKey(key, opFact instanceof BinaryOperationFactory);
    addOperation(key, o);
  }
Enqueue the given {@link Operation} with the used key.

@param key the key to use.
@param o the {@link Operation} to enqueue.
src/main/java/net/spy/memcached/MemcachedConnection.java