Re: End of Stream
Milad wrote:
this program read stream and print it through System.ou
try {
FileInputStream fis = new FileInputStream("README.TXT");
int n;
while ((n = fis.available()) > 0) {
byte[] b = new byte[n];
int result = fis.read(b);
if (result == -1) break;
String s = new String(b);
System.out.print(s);
} // End while
} // End try
catch (IOException e) {System.err.println(e);}
System.out.println();
why this code use blow line??
if (result == -1) break;
Are you asking why this line is there? If so, it's there to prevent getting
an end-of-file (EOF) that will mess up the following lines.
If I comment this line in this program the program work without any
problem:
A more accurate statement is that the program will sometimes work without
trouble with the line commented out (deleted).
There are some problems with the code that I see.
- available() only returns an estimate of how many bytes one can read from the
stream without blocking. The estimate may be wrong. There also could be more
bytes available by the time you perform the read(). The docs for available()
tell us that "[a] single read or skip of this many bytes will not block, but
may read or skip fewer bytes" than available() estimated.
- available() might return 0 one moment, and more bytes might become available
in the next moment. If you stop the loop when available() returns 0, you
might miss some data.
- setting 'b' to be of length 'n' doesn't mean that 'n' bytes will actually be
read. In this particular loop, if it doesn't end prematurely, the remaining
bytes will be picked up in the next iteration, but you can't always count on
that in every program.
- setting String 's' to 'new String(b)' might give gobbledygook if the read()
call returned fewer than 'n' bytes.
- setting String 's' to 'new String(b)' might give gobbledygook if the file is
not in the same character encoding as your platform's default encoding.
- setting String 's' to 'new String(b)' might give gobbledygook if the read()
call didn't return an exact number of characters from the file. Many files
use multi-byte encodings.
The usual idiom in Java, using while() and not the alternative for() loop, is
like this (ignoring exceptions):
FileReader in = new FileReader( "README.TXT" );
char [] b = new char [BUFFER_SIZE];
int n;
while ( (n = in.read( b )) >= 0 )
{
String s = new String( b, 0, n );
System.out.print( s );
}
System.out.println();
With a for() loop you can restrict the scope of the int 'n' to the loop.
--
Lew