Java IO.pdf - Nguyen Dang Binh

Java I/O
System.out, System.err, and some (but not all) other print streams automatically flush after
each call to println() and after each time a new line character ('\n') appears in the string
being written. Whether auto-flushing is enabled can be set in the PrintStream constructor.
2.5 Subclassing OutputStream
OutputStream is an abstract class that mainly describes the operations available with any
particular OutputStream object. Specific subclasses know how to write bytes to particular
destinations. For instance, a FileOutputStream uses native code to write data in files. A
ByteArrayOutputStream uses pure Java to write its output in a potentially expanding byte
array.
Recall that there are three overloaded variants of the write() method in OutputStream, one
abstract, two concrete:
public abstract void write(int b) throws IOException
public void write(byte[] data) throws IOException
public void write(byte[] data, int offset, int length) throws IOException
Subclasses must implement the abstract write(int b) method. They often choose to override
the third variant, write(byte[], data int offset, int length), for reasons of
performance. The implementation of the three-argument version of the write() method in
OutputStream simply invokes write(int b) repeatedly; that is:
public void write(byte[] data, int offset, int length) throws IOException {
for (int i = offset; i < offset+length; i++) write(data[i]);
}
Most subclasses can provide more efficient implementations of this method. The oneargument
variant of write() merely invokes write(data, 0, data.length); if the threeargument
variant has been overridden, this method will perform reasonably well. However, a
few subclasses may override it anyway.
Example 2.3 is a simple program called NullOutputStream that mimics the behavior of
/dev/null on Unix operating systems. Data written into a null output stream is lost.
Example 2.3. The NullOutputStream Class
package com.macfaq.io;
import java.io.*;
public class NullOutputStream extends OutputStream {
}
public void write(int b) { }
public void write(byte[] data) { }
public void write(byte[] data, int offset, int length) { }
By redirecting System.out and System.err to a null output stream in the shipping version of
your program, you can disable any debugging messages that might have slipped through
quality assurance. For example:
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