RAMFile() 
{
  // File used as buffer, in no RAMDirectory
}

 RAMFile(RAMDirectory directory) 
{
    this.directory = directory;
}

 final synchronized byte[] addBuffer(int size) 
{
    byte[] buffer = newBuffer(size);
    if (directory!=null)
      synchronized (directory) {             // Ensure addition of buffer and adjustment to directory size are atomic wrt directory
        buffers.add(buffer);
        directory.sizeInBytes += size;
        sizeInBytes += size;
      }
    else
      buffers.add(buffer);
    return buffer;
}

 final synchronized byte[] getBuffer(int index) 
{
    return (byte[]) buffers.get(index);
}

 synchronized long getLastModified() 
{
    return lastModified;
}

 synchronized long getLength() 
{
    return length;
}

 long getSizeInBytes() 
{
    synchronized (directory) {
      return sizeInBytes;
    }
}

 byte[] newBuffer(int size) 
{
    return new byte[size];
}

Expert: allocate a new buffer. Subclasses can allocate differently.

 final synchronized int numBuffers() 
{
    return buffers.size();
}

 synchronized  void setLastModified(long lastModified) 
{
    this.lastModified = lastModified;
}

 synchronized  void setLength(long length) 
{
    this.length = length;
}