Java Reference
In-Depth Information
of these might be thrown. Instances of checked subclasses of IOException may be thrown
at times to provide more-detailed diagnostic information, such as FileNotFoundException
and EOFException . From Java 7, a shift is taking place from a number of classes in the java.
io package to those in the java.nio hierarchy, although without completely superseding eve-
rything in . We will introduce some of these new classes alongside the legacy ones.
A full description of the many different classes in the and java.nio packages is
beyond the scope of this topic, but we shall provide some fundamental examples within the
context of several of the projects we have already seen. This should give you enough back-
ground to experiment with input/output in your own projects. In particular, we shall illustrate
the following common tasks:
obtaining information about a file from the file system
writing textual output to a file with the FileWriter class
reading textual input from a file with the FileReader and BufferedReader classes
anticipating IOException exceptions
parsing input with the Scanner class
In addition, we look at reading and writing binary versions of objects as a brief introduction to
Java's serialization feature.
For further reading on input/output in Java, we recommend Oracle's tutorial, which can be
found online at:
Readers, writers, and streams
Several of the classes of the package fall into one of two main categories: those
dealing with text files and those dealing with binary files. We can think of text files as contain-
ing data in a form similar to Java's char type—typically simple, line-based, human-readable
alphanumeric information. Web pages, written in HTML, are a particular example. Binary
files are more varied: image files are one common example, as are executable programs such
as word processors and media players. Java classes concerned with processing text files are
known as readers and writers , whereas those concerned with binary files are known as stream
handlers. In the main, we shall focus on readers and writers.
12.9.2 The File class and Path interface
A file is much more than just a name and some contents. A file will be located in a particular
folder or directory on a particular disk drive, for instance, and different operating systems have
different conventions for which characters are used in file pathnames. The File class allows a
program to enquire about details of an external file in a way that is independent of the particular
file system on which the program is running. The name of the file is passed to the constructor of
File . Creating a File object within a program does not create a file in the file system. Rather,
it results in details about a file being stored in the File object if the external file exists.
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