Java IO.pdf - Nguyen Dang Binh

Chapter 13
Chapter 14
Chapter 15
Chapter 16
Java I/O
not only how to use the File class, but also the precautions you need to take to make
your file code portable across all major platforms that support Java.
Filenames are problematic, even if you don't have to worry about cross-platform
idiosyncrasies. Users forget filenames, mistype them, can't remember the exact path to
files they need, and more. The proper way to ask a user to choose a file is to show
them a list of the files and let them pick one. Most graphical user interfaces provide
standard graphical widgets for selecting a file. In Java, the platform's native file
selector widget is exposed through the java.awt.FileDialog class. Like many
native peer-based classes, however, FileDialog doesn't behave the same or provide
the same services on all platforms. Therefore, the Java Foundation Classes 1.1
(Swing) provide a pure Java implementation of a file dialog, the
javax.swing.JFileChooser class. Chapter 13 shows you how to use both these
classes to provide a GUI file selection interface. In the final example, you'll add a
Swing-based GUI to the File Viewer program.
We live on a planet where many languages are spoken, yet most programming
languages still operate under the assumption that everything you need to say can be
expressed in English. Java is starting to change that by adopting the multinational
Unicode as its native character set. All Java chars and strings are given in Unicode.
However, since there's also a lot of non-Unicode legacy text in the world, in a
dizzying array of encodings, Java also provides the classes you need to read and write
this text in these encodings as well. Chapter 14 introduces you to the multitude of
character sets used around the world, and develops a simple applet to test which ones
your browser/VM combination supports.
A language that supports international text must separate the reading and writing of
raw bytes from the reading and writing of characters, since in an international system
they are no longer the same thing. Classes that read characters must be able to parse a
variety of character encodings, not just ASCII, and translate them into the language's
native character set. Classes that write characters must be able to translate the
language's native character set into a variety of formats and write those. In Java, this
task is performed by the Reader and Writer classes. Chapter 15 shows you how to
use these classes, and adds support for multilingual text to the File Viewer program.
Java 1.0 did not provide classes for specifying the width, precision, and alignment of
numeric strings. Java 1.1 and later make these available as subclasses of
java.text.NumberFormat. As well as handling the traditional formatting achieved by
languages like C and Fortran, NumberFormat also internationalizes numbers with
different character sets, thousands separators, decimal points, and digit characters.
Chapter 16 shows you how to use this class and its subclasses for traditional tasks, like
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