The I/O Package - The Java Programming Language - page 780

}
// ...
}
If there are no parameters, we use System.in for input. If there are para-
meters, we create an ArrayList large enough to hold as many BufferedIn-
putStream objects as there are command-line arguments (see " ArrayList "
on page 582 ) . Then we create a stream for each named file and add
the stream to the inputs list. When the loop is finished, we use the Col-
lections class's enumeration method to get an Enumeration object for the
list elements. We use this Enumeration in the constructor for SequenceIn-
putStream to create a single stream that concatenates all the streams for
the files into a single InputStream object. A simple loop then reads all the
bytes from that stream and writes them on System.out .
You could instead write your own implementation of Enumeration whose
nextElement method creates a FileInputStream for each argument on de-
mand, closing the previous stream, if any.
20.5.11. Pushback Streams
A Pushback stream lets you push back, or "unread," characters or bytes
when you have read too far. Pushback is typically useful for breaking in-
put into tokens. Lexical scanners, for example, often know that a token
(such as an identifier) has ended only when they have read the first
character that follows it. Having seen that character, the scanner must
push it back onto the input stream so that it is available as the start of
the next token. The following example uses PushbackInputStream to report
the longest consecutive sequence of any single byte in its input:
import java.io.*;
class SequenceCount {
public static void main(String[] args)
throws IOException