Hi Kim
You are right. In fact there are three methods to override. For e.g.:
-- Your Filter, inheriting FilterInputStream, has a constructor that
sets the "in" member. As it is protected, you can access it from your
derived class
-- Your overridden read() just makes something like char c =
Character.toUpperCase((char)in.Read());
-- The read(byte[] b) calls in.read(b), then converts all the bytes
(assumed to be characters) to upper cases
-- The read(byte[] b, int off, int len) calls in.read(b, off, len) then
converts to upper cases only the bytes between the offset and offset +
len. Something like:
for ( int i = 0 ; i < len ; i++ ){
b[off + i] = (byte)Character.toUpeerCase((char)b[off + i]);
}
Hope it helps
Mihai
Kim Ching Koh a écrit :
Hi Mihai,
Not sure what do you mean by read a buffer, do you mean *read*
<https://mail.google.com/mail/html/java/io/FilterInputStream.html#read%28byte%5B%5D%29>(byte[] b)?
How about *read*
<https://mail.google.com/mail/html/java/io/FilterInputStream.html#read%28byte%5B%5D,%20int,%20int%29>(byte[] b,
int off, int len)? Need to override too?
read(byte[] b) seems to be calling read(byte[] b, int off, int len),
so we maybe able to to override read(byte[] b) but I am not sure how
to override read(byte[] int off, int len)
In Exercise 8, read(byte[] int off int len) seem to calling itself?
How does this work?
public int read(byte[] b, int off, int len) throws IOException {
len = in.read(b, off, len);
if (len != -1) {
cksum.update(b, off, len);
}
return len;
}
Thanks.
KC
On Wed, May 26, 2010 at 2:15 PM, Mihai DINCA <[email protected]
<mailto:[email protected]>> wrote:
Hi Kim
The idea of the topic is that InputStreams and OutputStreams are
based on layers. Once you have an InputStream, you can read from
it through a filter. For e.g., you can write InputStream in = new
BufferedInputStream( new FileInputStream("filename.txt"));. The
FileInputStream is the actual source of data, but you read it
through a BufferedInputStream that allows a (more efficient)
buffered read from the source, still allowing a byte-by-byte access.
You can extend all this and write:
InputStream in = new MyFilter1Stream( new MyFilter2Stream( new
MyFilter3Stream( new FileInputStream("myfile.txt"))));
where each filter adds something to the reading process. One of
them might, for e.g., convert all the input characters to capital
letters.
The same idea applies to OutputStreams. You can have your own
filter in the chain that converts, for e.g., all the dirty words
in "***" strings.
The homework is based by a lab exercise that reads from a file,
through and InputStream, and echoes its contents to another one,
through an OutputStream and asks to write other a filter for the
input or a filter for the output that converts all letters to
capital letters.
To create your own FilterInputStream, you must override both read
methods (the one that read on byte and the other that reads a
buffer) so that they read from the source InputStream (one byte or
a buffer), then convert the input to capital letters.
Analogically, to create your own FilterOutputStream yo must
override all the write methods.
Hope it helps
Mihai
Kim Ching Koh a écrit :
Hi,
Anyone has done this homework can advise?
Regards
KC
On Tue, May 25, 2010 at 2:53 PM, kc <[email protected]
<mailto:[email protected]>> wrote:
Hi,
I am not too sure what is the requirement of the homework for
java
stream I/O, is it just to overide read() in the
ChangeToUpperCaseInputStream class so it will convert and
return to
uppercase?
1. The homework is to either modify FilterInputOutputStream
NetBeans
project you've done in Exercise 8 above or create a new
project as
following. (You might want to create a new project by
copying the
FilterInputOutputStream project. You can name the homework
project in
any way you want but here I am going to call it
MyIOStreamProject.)
Write ChangeToUpperCaseInputStream class, which extends
FilterInputStream.
Write ChangeToUpperCaseOutputStream class, which extends
FilterOutputStream.
Use either ChangeToUpperCaseInputStream class or
ChangeToUpperCaseOutputStream class to convert the characters
read to
upper case.
Regards
KC
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