Java IO.pdf - Nguyen Dang Binh

;
}
Java I/O
public int read(byte[] data, int offset, int length) throws IOException {
}
int result = in.read(data, offset, length);
for (int i = offset; i < offset+result; i++) {
// Do nothing with the printing characters.
if (data[i] == 10 || data[i] == 13 || data[i] == 9 || data[i] == -1)
// nonprinting characters
else if (data[i] < 32 || data[i] > 126) data[i] = (byte) '?';
}
return result;
6.2 The Filter Stream Subclasses
The java.io package contains many useful filter stream classes. The BufferedInputStream
and BufferedOutputStream classes buffer reads and writes by first putting data into a buffer
(an internal array of bytes). Thus, an application can read or write bytes to the stream without
necessarily calling the underlying native methods. The data is read from or written into the
buffer in blocks; subsequent accesses go straight to the buffer. This improves performance in
many situations. Buffered input streams also allow the reader to back up and reread data.
The java.io.PrintStream class, which System.out and System.err are instances of,
allows very simple printing of primitive values, objects, and string literals. It uses the
platform's default character encoding to convert characters into bytes. This class traps all
IOExceptions and is primarily intended for debugging. System.out and System.err are the
most popular examples of the PrintStream class, but you can connect a PrintStream filter
to other output streams as well. For example, you can chain a PrintStream to a
FileOutputStream to easily write text into a file.
The PushbackInputStream class has a one-byte pushback buffer so a program can "unread"
the last character read. The next time data is read from the stream, the unread character is
reread.
The DataInputStream and DataOutputStream classes read and write primitive Java data
types and strings in a machine-independent way. (Big-endian for integer types, IEEE-754 for
floats and doubles, UTF-8 for Unicode.) These are important enough to justify a chapter of
their own and will be discussed in the next chapter. The ObjectInputStream and
ObjectOutputStream classes extend DataInputStream and DataOutputStream with
methods to read and write arbitrary Java objects as well as primitive data types. These will be
taken up in Chapter 11.
The java.util.zip package also includes several filter stream classes. The filter input
streams in this package decompress compressed data; the filter output streams compress raw
data. These will be discussed in Chapter 9.
The java.util.security package contains the DigestInputStream and
DigestOutputStream filter streams; these calculate message digests of the data that passes
through them. Installing the Java Cryptography Extension (JCE) adds two more filter streams
to this package, CipherInputStream and CipherOutputStream , which can encrypt or
decrypt data using a variety of algorithms. These will be discussed in Chapter 10.
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