Re: operator overloading

John W Kennedy <>
Fri, 09 May 2008 20:02:36 -0400
Tom Anderson wrote:

I think i was doing something where i needed to be able to read lines of
text, but also things in binary, from a stream. To read lines, you need
a BufferedReader, and to read binary data, you need a DataInputStream;
you can wrap the BufferedReader round an InputStreamReader, and wrap
that round the DataInputStream, or whatever stream underlies that. But
then you have a problem, because the BufferedReader is eating more the
data than it should. DataInputStream has a readLine of its own, but it'd
deprecated and doesn't do character encoding.

More generally, i just don't see why there needs to be a Reader/Writer
hierarchy that parallels the InputStream/OutputStream hierarchy. Why not
just have a Reader, which wraps an InputStream and does decoding, and a
Writer, which wraps an OutputStream and does encoding? The Reader would
be able to read lines, but only if on top of a PushbackInputStream. That
would have solved my problem in a trice.

I guess there's a case for StringReader/StringWriter too. But not the
File/Buffered/whatever ones. Byte streams can provide those facilities.

The problem is that what you're asking for covers only a handful of
cases: those in which binary data gets mixed with LF-terminated (or CRLF
or CR) string data. It does not cover cases where the string data is
embedded in the binary data, which is far more common in the real world.
The normal way to handle it is:

    final DataInputStream dis = new DataInputStream(...);
    final CharSet cs = CharSet.forName("ISO-8859-1");
    final byte[] ba = new byte[32];
    for (;;) {
       final String st = new String(ba, cs);

or, for variable-length strings, probably something like:

    for (;;) {
       final short l = dis.readShort();
       final byte[] ba = new byte[l];
       final String st = new String(ba, cs);

(Exception: if your file is /only/ to be read and written by Java, the
WriteUTF and ReadUTF may be appropriate.)
John W. Kennedy
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