code: private void writeObject (ObjectOutputStream s)
          throws IOException
      {
          // write out number of buckets
          s.writeInt(_buckets.length);
          s.writeFloat(_loadFactor);
  
          // write out size (number of mappings)
          s.writeInt(_size);
  
          // write out keys and values
          for (IntIntEntry entry : entrySet()) {
              s.writeInt(entry.getIntKey());
              s.writeInt(entry.getIntValue());
          }
      }
docs: Save the state of this instance to a stream (i.e., serialize it).