Input and Output - Java - page 373

Solution

Use a StreamTokenizer , readLine() , and a StringTokenizer ; the Scanner class (see
Scanning Input with the Scanner Class ) ; regular expressions ( Chapter 4 ) ; or one of several
third-party “parser generator” tools.

Discussion

Though you could, in theory, read a file one character at a time and analyze each character,
that is a pretty low-level approach. The read() method in the Reader class is defined to re-
turn int so that it can use the time-honored value -1 (defined as EOF in Unix <stdio.h> for
years) to indicate that you have read to the end of the file:

src/main/java/io/ReadCharsOneAtATime.java

public public class class ReadCharsOneAtATime ReadCharsOneAtATime {

void void doFile ( Reader is ) throws throws IOException {

int int c ;

while while (( c = is . read ( )) != - 1 ) {

System . out . print (( char char ) c );

}

}

}

The cast to char is interesting. The program compiles fine without it, but does not print cor-
rectly because c is declared as int (which it must be, to be able to compare against the end-
of-file value -1 ). For example, the integer value corresponding to capital A treated as an int
prints as 65, whereas (char) prints the character A .

We discussed the StringTokenizer class extensively in Breaking Strings Into Words . The
combination of readLine() and StringTokenizer provides a simple means of scanning a
file. Suppose you need to read a file in which each line consists of a name like
[e-mail] , and you want to split the lines into users and host addresses. You could
use this:

public public class class ScanStringTok ScanStringTok {

protected protected LineNumberReader is ;

public public static static void void main ( String [] av ) throws throws IOException {