Java Reference
In-Depth Information
This code would replace the comment in the previous fragment that appears at the beginning of the
while
loop. You first create a
StringBuffer
object in which you assemble the string. This is the most efficient
way to do this — using a
String
object would result in the creation of a new
String
object each time
you add a character to the string. Of course, because there's no possibility of multiple threads accessing the
string, you could use a
StringBuilder
object here instead of the
StringBuffer
object and gain a little
more efficiency. The
remaining()
method for the buffer returns the number of bytes read after the buffer
has been flipped, so you can just divide this by two to get the number of characters read. You extract char-
acters one at a time from the buffer in the
while
loop and append them to the
StringBuffer
object. The
getChar()
method increments the buffer's position by two each time, so eventually the
hasRemaining()
method returns
false
when all the characters have been extracted, and the loop ends. You then just convert
the
StringBuffer
to a
String
object and output the string on the command line.
This approach works okay, but a better way is to use a view buffer of type
CharBuffer
. The
toString()
method for the
CharBuffer
object gives you the string that it contains directly. Indeed, you can boil the
whole thing down to a single statement:
System.out.println("String read: " +
((ByteBuffer)(buf.flip())).asCharBuffer().toString());
The
flip()
method returns a reference of type
Buffer
, so you have to cast it to type
ByteBuffer
to
make it possible to call the
asCharBuffer()
method for the buffer object. This is necessary because the
asCharBuffer()
method is defined in the
CharBuffer
class, not in the
Buffer
class.
You can assemble these code fragments into a working example.
TRY IT OUT: Reading Text from a File
Here's the code for the complete program to read the
charData.txt
file that you wrote in the previous
chapter using the
BufferStateTrace.java
program:
import java.nio.file.*;
import java.nio.channels.ReadableByteChannel;
import java.io.IOException;
import java.nio.ByteBuffer;
public class ReadAString {
public static void main(String[] args) {
Path file = Paths.get(System.getProperty("user.home")).
resolve("Beginning Java
Stuff").resolve("charData.txt");
if(!Files.exists(file)) {
System.out.println(file + " does not exist. Terminating
program.");
System.exit(1);;
