A file output stream is an output stream for writing data to a <code>File</code> or to a <code>FileDescriptor</code>. Whether or not a file is available or may be created depends upon the underlying platform. Some platforms, in particular, allow a file to be opened for writing by only one {@code FileOutputStream} (or other file-writing object) at a time. In such situations the constructors in this class will fail if the file involved is already open.