Programs use byte streams to perform input and output of 8-bit bytes. All byte stream classes are descended fromInputStream
andOutputStream
.There are many byte stream classes. To demonstrate how byte streams work, we'll focus on the file I/O byte streams,
FileInputStream
andFileOutputStream
. Other kinds of byte streams are used much the same way; they differ mainly in the way they are constructed.Using Byte Streams
We'll exploreFileInputStream
andFileOutputStream
by examining an example program namedCopyBytes
, which uses byte streams to copyxanadu.txt
, one byte at a time.import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; public class CopyBytes { public static void main(String[] args) throws IOException { FileInputStream in = null; FileOutputStream out = null; try { in = new FileInputStream("xanadu.txt"); out = new FileOutputStream("outagain.txt"); int c; while ((c = in.read()) != -1) { out.write(c); } } finally { if (in != null) { in.close(); } if (out != null) { out.close(); } } } }CopyBytes
spends most of its time in a simple loop that reads the input stream and writes the output stream, one byte at a time, as shown in the following figure.Notice that Simple byte stream input and output.
read()
returns anint
value. If the input is a stream of bytes, why doesn'tread()
return abyte
value? Using aint
as a return type allowsread()
to use -1 to indicate that it's reached the end of the stream.Always Close Streams
Closing a stream when it's no longer needed is very important — so important thatCopyBytes
uses afinally
block to guarantee that both streams will be closed even if an error occurs. This practice helps avoid serious resource leaks.One possible error is that
CopyBytes
was unable to open one or both files. When that happens, the stream variable corresponding to the file never changes from its initialnull
value. That's whyCopyBytes
makes sure that each stream variable contains an object reference before invokingclose
.When Not to Use Byte Streams
CopyBytes
seems like a normal program, but it actually represents a kind of low-level I/O that you should avoid. Sincexanadu.txt
contains character data, the best approach is to use character streams. There are also streams for more complicated data types. Byte streams should only be used for the most primitive I/O.So why talk about byte streams? Because all other stream types are built on byte streams.