org.linkedin.util-core/src/main/java/org/linkedin/util/io/ram/RAMDirectory.java
public RAMDirectory mkdir(String name) throws IOException
  {
    RAMEntry entry = getEntry(name);
    if(entry instanceof RAMDirectory)
    {
      RAMDirectory ramDirectory = (RAMDirectory) entry;
      return ramDirectory;
    }
    else
    {
      if(entry == null)
      {
        RAMDirectory directory = new RAMDirectory(_clock, name);
        return (RAMDirectory) add(directory);
      }
      else
      {
        throw new IOException("File exists: " + name);
      }
    }
  }
public RAMDirectory mkdir(String name) throws IOException
  {
    RAMEntry entry = getEntry(name);
    if(entry instanceof RAMDirectory)
    {
      RAMDirectory ramDirectory = (RAMDirectory) entry;
      return ramDirectory;
    }
    else
    {
      if(entry == null)
      {
        RAMDirectory directory = new RAMDirectory(_clock, name);
        return (RAMDirectory) add(directory);
      }
      else
      {
        throw new IOException("File exists: " + name);
      }
    }
  }
Creates an empty directory and add it to this directory with this name. If the directory
already exists, it does not recreate it.

@param name
@return the created directory
@throws IOException if the name represents a file